The in-form attacking midfielder has joined the Gelsenkirchen side on a four-year deal
General manager Horst Heldt confirmed on Friday that the Ghana international has signed a four-year deal with the Bundesliga side.
Schalke have endured a rocky start to the 2013-14 season, and Heldt feels that the attacking midfielder can help get the Gelsenkirchen outfit back on the right path.
"He is a player with exceptional qualities and a great leader," Heldt told a press conference. "It was easy convincing the player to come – the challenge with the transfer came in convincing Milan to part with him.
"He will wear the No.9 jersey."
Meanwhile, coach Jens Keller, who has struggled to produce good results since pre-season, feels the addition of the 26-year-old will help propel his side in the right direction.
He continued: "He has a wealth of international experience which will greatly benefit our team."
Keller added that he is hopeful of using the former Borussia Dortmund attacker in his squad to face Bayer Leverkusen on Saturday.