By DAVID COVERDALE
The former Chelsea hitman was in the Galatasaray side that drew 1-1 with the Germans in last night’s last-16 tie in Istanbul.
It was Drogba’s first Champions League appearance since helping the Blues beat Bayern Munich in last year’s final.
But the Ivorian is facing claims that he should not have been allowed to play in the game.
The Bundesliga club wrote in a statement: “There are doubts about the validity of the permission to play for Drogba in the Champions League.
“Schalke 04 reserves its rights and is looking into this.”
Drogba is on an 18-month loan deal at Galatasaray from Chinese side Shanghai Shenhua.