Ballack joined the Blues on a free transfer in the summer of 2006. He arrived with a reputation as one of the world's standout midfielders and joined a Chelsea squad that had claimed the Premier League title in the previous two years.

He would spend four seasons at Stamford Bridge, during which he helped the club claim further silverware, although the trophy he desired most painfully alluded the former midfielder.

How do you remember the summer of 2006?

'I had been playing for four years at Bayern and my big target was winning the Champions League. Chelsea were structuring the club in a new way, investing in players and having the biggest targets a player can have.

'That combination was why I saw my future with the club, and living in London with my family was another reason for me to choose Chelsea. I joined the club after they had won the league for two seasons, but they also wanted to win international titles.'

Did you have any preconceptions about English football, and was it the same as you thought it would be when you started playing for Chelsea?

'Of course, there was a kind of expectation that the football was tough, physically, but I was always confident I could adapt well because of my style of play.

'I thought I suited English football, and then when I came over and started playing, what I expected came even more true because the referees didn’t whistle too much for free-kicks, there were a lot of challenges, and it was physically a much stronger level than all other leagues.

'I had played in Germany for many years and when you play in the Champions League against Spanish teams or Italian teams, you get a good idea of other leagues. English football was more physical; it was as I expected, to be honest.'

There were a lot of players in the Chelsea squad with you who were captains of their national teams. Had you ever played for a team with so many leaders?

'No, that wasn’t normal. It was an exception and, at times, it was a delicate situation, especially for the coach who had to handle these big characters. It’s not always easy, but I think we did well, overall, and we had the intelligence that you need to step back in certain situations.

'You don’t have to lead all the time, maybe like it was before, when I played for clubs that had one, two, maximum three, leaders, and it was always down to them to handle difficult situations. We had a lot of leaders at Chelsea, but I was sure we could push each other all the time, not just in the games but also in training. There was always another one who could have an impact.

'There were so many characters – not just the captains, but in general, it was a squad with very strong characteristics. The main thing was to have a strong coach to deal with all these players, to make it work, and to put the energy of each one in the right direction.

'There’s a small difference between going the right way and going in a way that creates problems in that situation. When you have these characters and you’re not playing 100 per cent well, it can create trouble. But I had the feeling, over my four years, that was never the case. All the coaches handled it really well.'

You arrived at Chelsea as an already experienced player and a complete midfielder, but did you learn anything new during your four years here?

'Yes, of course, I learned always. It was a completely new situation for me because I had always played in Germany. I had this view from the players, the media and the fans in Germany, but now I had moved to another country and I started again, not quite from zero, but it was new.

'You learn different ways of training, preparation, the English mentality, so you have to adapt. But at the same time, you are trying to bring your German ideas, and your team-mates bring other things from other places as well.

'Each club and each country has its own traditions, its own identity, its own atmosphere during the matches – that’s what made my time at Chelsea so special. It was totally different than what I had experienced before. You are surrounded by all these players from different national teams and you pick up a bit from everybody around you.'

When did you feel at your best during those four years at Chelsea?

'I felt pretty comfortable a few months after I had recovered from my injury in 2007/08. I had a difficult time coming back at first under Jose Mourinho. I wanted to play but I couldn’t. So, after the injury, I was very motivated to play, by that point, under Avram Grant.

'I think I had a good time in that period. I can’t explain it, but I felt really good as we went to the Champions League final that season. That was a great period for me, but also the next season – 2008/09 – when we went out in the semi-final to Barcelona.

'We probably had our strongest period in March and April of that season. We looked so strong and I really thought it was our best period in my time at Chelsea. Even without winning the league, in the Champions League, we were really, really good and were unlucky not to win it that year.

'I would also mention my last season under Carlo Ancelotti, when we scored so many goals and also looked so comfortable. I had a slightly deeper role in midfield, in front of the defenders, and we played very good football as we won the Double that year.'

If you look at the set-ups of the team you joined in 2006 and the team you left in 2010, they were completely different in their approach, weren’t they?

'Yeah, that’s true. We felt really comfortable in our game. Under Jose, we were well-organised and everyone knew what he had to do. It was more relaxed football in my last year under Ancelotti – an Italian coach with so much experience of handling big players and getting the best out of them.

'I think you could see that each player was really free and also the knowledge was good – players accepted their roles and he handled the whole squad really well. You could see that we were scoring so many goals and it was really enjoyable to watch us.'

You mentioned those couple of months towards the end of the 2008/09 season – under Guus Hiddink – when you felt we were playing some of our best football. Let’s talk about the Barcelona defeat in the Champions League semi-final when two great teams met in a great match, and the referee also had a big say in the outcome. Does that stand out in your memory?

'Yes, because we were so full of confidence at that time and we played against a fantastic Barcelona side. In the second leg, especially at Stamford Bridge, we had them under so much control. We always felt we would win that game and reach the final.

'But somehow the referee... he had a bit of an impact! There’s no doubt it was really frustrating. You know you are the better team, and then you also can’t really react after you concede a goal as late as we did. They scored in the 90th minute, although I remember we had one or two chances even after that – we looked so strong.

'At that time, it seemed like we always had another gear we could pull into, but that night was frustrating, especially as there was such a strong atmosphere in the dressing room, a comfortable atmosphere between the players.

'When we looked at each other, we knew we would win. There was a feeling at the club that we couldn’t lose. It was unique.

'But that was just one of those matches where you think, “Why did the referee make such decisions?” But that is football and you have to accept it, even if it was frustrating at the time, especially after what happened the year before in the final.'

Was losing that 2008 final in Moscow an even worse feeling?

'Of course. If it comes down to one shot, it’s the worst situation in football for you as a player. But we came back and I think we were even stronger the year after, so going out again in the way we did against Barcelona... yeah... as I mentioned, it was pretty frustrating. I think that team deserved to win the Champions League.'

You did win every major domestic trophy during your time at Chelsea, and you contributed in big moments, such as your winning goal against Blackburn in the 2007 FA Cup semi-final, or your brace against Manchester United at Stamford Bridge in April 2008...

'Sometimes you have to do this, even if you don’t play at your best, you do something to make sure you win the important games. I think, overall, during my time at big clubs, the players understood that. That’s why these kinds of players play for the big clubs.

'Mentally, they have that little bit extra to understand and to deliver at the right time. You can’t always play at your best – that’s not possible – but if you can’t do that, you can find that little bit extra to change the game.'

Finally, how significant would you say your time at Chelsea was when you reflect on your career as a whole?

'It was really important because it gave me a different view of everything: the language, playing internationally, how the fans looked at me. When I go around the world, it’s Bayern, but I think it’s even more so Chelsea that people remember.

'The Premier League is seen all over the world, so people watched you and, even more, people respected you. Personally, I felt really comfortable there. Life was good. I enjoyed living in London and playing for Chelsea – it was a fantastic four years for me.'