Schalke defender Benedikt Howedes will be given every possible chance to recover from his stomach strain.
The Germany Under-21 star was a goalscorer in Schalke's quarter-final win over Inter Milan and coach Ralf Rangnick knows he will have to reshape his entire starting line-up if Howedes does not make it.
There was better news about Kyriakos Papadopoulous and Peer Kluge, who have both recovered from minor problems and will be available.
Sir Alex Ferguson is hoping to break new ground by steering Manchester United past German opposition in a two-legged European encounter.
After four previous failures as United boss, Ferguson is hoping to make it fourth time lucky in the Champions League semi-final against Schalke.
Dimitar Berbatov (groin) and Darren Fletcher (virus) are out, otherwise the Red Devils manager is selecting from strength.
Schalke (from): Neuer, Schober, Sarpei, Escudero, Howedes, Plestan, Papadopoulous, Metzelder, Uchida, Hao, Baumjohann, Kluger, Schmitz, Jurado, Diac, Draxier, Matip, Raul, Edu, Charisteas, Farfan.
Man Utd (from): Van der Sar, Kuszczak, Rafael, O'Shea, Brown, Ferdinand, Smalling, Vidic, Evans, Evra, Fabio, Valencia, Gibson, Anderson, Park, Carrick, Giggs, Nani, Rooney, Hernandez, Owen.