Jose Mourinho is hopeful of having some of his injured players available for Sunday's crunch Premier League clash with Liverpool.
Marcos Rojo joined the injured ranks during Wednesday's Champions League loss to Valencia, and defence is the biggest worry for Mourinho with Chris Smalling, Diogo Dalot, Matteo Darmian, Luke Shaw and Victor Lindelof also struggling.
Mourinho said: "All of them didn't train yesterday again. Today there will be a little introduction to see the answer and to see if we can increase a little bit tomorrow to have them available for Sunday. I hope some will be available but for sure some will not be."
United head to Anfield to face the Premier League leaders with "doubts about everything" because of the uncertainty of who will be fit.
Mourinho added: "We know that we are going to play against the leader, against a team on a high. But we have our qualities, we have our potential, and even with the problems we have and the doubts in terms of team choice, of tactics, approach, philosophy.
"We have doubts about everything because we don't know who's available but we are going to arrive on Sunday, and with the players we have available, we are going to have a team capable of going there and fight for the victory."
