Manchester boss Louis Van Gaal has admitted he doesn't know who to start against Middlesbrough and that many of his players are in the 'red zone' in terms of fatigue.
The Red Devils face the Championship side in the fourth round of the Capital One Cup on Wednesday might and are currently without the services of injured trio Luke Shaw, Paddy McNair and Antonio Valencia.
And, Van Gaal is wary of playing fatigued players as he fears losing more first-team players to injury.
"I have a lot of players in the red zone, because we have had a lot of matches and we have a lot of matches to play," Van Gaal told the Guardian.
"I have to see if I can use them or not. We need all the days to recover at this moment."
"[Wilson and Pereira] are in the selection, but I have to select the lineup and that I don't know," Van Gaal said. "I have to do that tomorrow.
"I think Middlesbrough is a good playing side. They want to play football, that is also a benefit for us, I think. You can also see teams with another play style and that is more difficult for us, but we can play football against them but it is also dependable of the strategy their team."
United face The Boro after a 0-0 draw with fierce rivals Manchester City on Sunday and will be looking to get back to winning ways against Aitor Karanka's highly-rated side.