Radamel Falcao is only fit enough to play for 20 minutes, according to Manchester United boss Louis van Gaal.
The Colombian came off the bench in United's last two matches and Van Gaal said he "was not interested" if the striker was happy with that role.
Falcao, 28, is returning from a calf injury and has been pressed into action due to other injuries to the squad.
Dutchman Van Gaal said: "I have selected him in spite of the fact he can only play for 20 minutes."
With captain Wayne Rooney sidelined for Tuesday night's 2-1 win against Stoke, 19-year-old James Wilson started ahead of Falcao.
Van Gaal said: "It's match fitness [he needs].
"It would be a better contribution if he played with the second team but I cannot do that because on Tuesday we had the match against Stoke and Wayne Rooney was injured."
Falcao, who joined French club Monaco for a reported £50m in 2013 and is on loan at Old Trafford, is expected to be on the bench once again for Monday night's game against Southampton, with Van Gaal confirming Rooney will play.
Asked if the forward would be happy with a substitute's role, Van Gaal said: "I am not interested in that. He has to follow my philosophy."
Falcao, who missed much of last season with an anterior cruciate ligament injury, had a prolific goalscoring record at Atletico Madrid, FC Porto and Monaco but has netted just once in seven appearances for United.