The Bundesliga club – who were in dire need of an attacking midfielder – have signed the Croatia international for just €5 million, whilst his former club can re-sign the 20-year-old in the next two years for €10m, should they wish to do so.
Halilovic joined the Spanish club in the summer of 2014 from Dinamo Zagreb, but spent much of last season on loan at Sporting Gijon, where he made 36 appearances.
The Bundesliga club have moved fast to secure the signing of the Croatia international, who completed 81 dribbles last season, behind Neymar and Lionel Messi.
“He is an outstanding talent,” Hamburg CEO Dietmar Beiersdorfer told the club’s official website. “He feels situations, he feels the game. We are very pleased to welcome him.”
The 20-year-old told the website he is “very happy and proud” to have signed for a club of Hamburg’s stature.
“HSV is a great club,” added Halilovic. “I’ve spoken with my [international] teammate Milan Badelj. He has only told me good things, and now I can’t wait to get going.”
The Bundesliga club have struggled in the league of late, often battling relegation, but with the introduction of the Croatian, he hopes that he can help HSV get back to the top.
“I want to help Hamburg have a good season,” added Halilovic. “This is my job, and also my goal.
“We have a strong team here, and I hope that I can help continue to develop this team.”
A special number...
The youngster has opted to wear the number 23 for the coming season, a number which Rafael van der Vaart wore during his time at the club.
“I know that 23 has a special meaning,” added Halilovic. “Rafael van der Vaart was a great player for the club, and picking the number felt right for me.”