Schalke says it will lodge a complaint with UEFA over the 1-1 draw at Galatasaray in the Champions League because of Didier Drogba's participation.
The dpa news agency says Schalke sports director Horst Heldt and finance chief Peter Peters confirmed they would appeal over the player's eligibility before boarding Thursday's return flight from Istanbul.
Schalke wants UEFA to examine Drogba's switch from Shanghai Shenhua to the Turkish side - despite FIFA provisionally clearing Drogba to play last week.
Shanghai Shenhua complained to FIFA that Drogba broke his contract. Drogba, who had a contract through 2014, claims he was not being paid his salary.
If FIFA ruless for Shanghai Shenhua, the sanctions could see Drogba banned and a transfer embargo imposed on Galatasaray.