The goalkeeper's arrival was announced on 1 September 2010, though he was promptly loaned out to Vitesse Arnhem in Holland, joining up with fellow Chelsea youngsters, the Serbian pair of Slobodan Rajkovic and Nemanja Matic.
That brought him back to Cobham with a desire for first-team football, and so a loan move to Czech top division side SK Dynamo Ceske Budejovice, where he made five appearances, was agreed for the 2011/12 season.
He went on loan to Vitoria Guimaraes at the start of the 2012/13 season in Portugal before returning on loan at his former club, Inter Zapresic in Croatia.
Delac had earlier signed a pre-contract agreement to join Chelsea from Inter Zapresic, where he had already become first-choice goalkeeper despite his tender years.
Delac has represented the Croatia national side at every age group from Under-15s upwards. He was called into the senior squad by Slaven Bilic in August 2009 for the 2010 World Cup qualifiers against England and Belarus, breaking the record for the youngest Croatian ever called up for international duty.