Madrid - Schalke 04 have injury concerns over four players, including Benedikt Hoewedes and Klaas-Jan Huntelaar, for Tuesday's Champions League game at Real Madrid.
Defender Howedes and former Real striker Huntelaar picked up knocks in Saturday's 3-1 Bundesliga win at home to Hoffenheim along with midfielder Marco Hoeger and forward Eric Maxim Choupo-Moting.
"Who will be able to play will be decided after the final training session," coach Roberto Di Matteo told a news conference on Monday.