Sir Alex Ferguson has confirmed Wayne Rooney is a doubt for United.
Ferguson reported Rooney has "a tight hamstring" and the forward will be monitored before the United boss finalises his line-up. Dimitar Berbatov and Michael Owen are both in contention to start if Rooney fails to make it.
Darren Fletcher will play some part after recovering from the virus that has kept him out for two months, although, with his side two goals up from the first-leg, Ferguson will have Sunday's Premier League showdown with Chelsea in his mind when he makes his selection.
Defender Fabio has failed to recover from a knock sustained against Arsenal but goalkeeper Anders Lindegaard has recovered from a knee ligament injury after two months on the sidelines and is in the squad.
Schalke defender Benedikt Howedes has been out for two games with an abdominal strain, but coach Ralf Rangnick is considering picking the 23-year-old.
"The last four games he played we won," he said. "But this is not the last game of the season.
"He has to be 100% fit and we will listen to medical staff because we don't want to take a risk and find out that he will be missing for another three or four weeks."
Manchester United (from): Van der Sar, Kuszczak, Lindegaard, Rafael, O'Shea, Ferdinand, Vidic, Smalling, Evans, Brown, Evra, Valencia, Scholes, Anderson, Carrick, Fletcher, Gibson, Park, Giggs, Nani, Obertan, Rooney, Berbatov, Owen, Hernandez.