Morgan Schneiderlin has emerged as a doubt for Manchester United's Champions League match against CSKA Moscow.
The midfielder played the entirety of United's 0-0 draw at Crystal Palace on Saturday but missed the open part of the squad's final training session because of "personal reasons" before their meeting with CSKA at Old Trafford.
Right-back Antonio Valencia is expected to miss the Group B encounter because of a foot problem while Luke Shaw (leg) and Paddy McNair (abdomen) are sidelined by their respective long-term injuries.
Defender Phil Jones is available after overcoming his injury, but Memphis Depay is not available and James Wilson is also expected to be absent after missing training on Monday morning.
Centre-back Axel Tuanzebe, 17, trained with the squad.
A win over CSKA on Tuesday will keep United on course for qualification to the knockout stages.
The two teams played out a 1-1 draw when they met a fortnight ago in the reverse fixture. United have failed to score since Anthony Martial's diving header in the Arena Khimki.
Louis van Gaal's side drew 0-0 in the Manchester derby and recorded the same scoreline against Palace.
United also crashed out of the Capital One Cup to Middlesbrough on penalties last week following a goalless 120 minutes against the Championship club.