Hamburg have found a replacement for Son Heungmin, who has moved to Bayer Leverkusen, by signing Jacques Zoua from FC Basel.
He is reunited with his former Basel coach Thorsten Fink, who is now in charge of Hamburg, and becomes the Bundesliga side's first new arrival this summer.
"I'm delighted to be here, at this great club, in this great city," he said on his new club's website.
"HSV are a great club and the Bundesliga is a big thing for me, but Thorsten Fink was certainly one of the reasons why I chose to come here.
"HSV want to challenge for a place in Europe and that is what I want too. I can't wait to fight for this goal with my team."
The 21-year-old spent two of his four years with Basel working under Fink and made a total of 86 appearances for the Swiss champions.