Manchester United will assess Wayne Rooney to discover the extent of his knee injury after the striker was hurt in the 3-0 loss to Everton at Goodison Park.
Rooney came off in the closing minutes of United's heaviest league defeat under Louis van Gaal and was replaced by Robin van Persie, who made his first appearance for two months.
Manager Van Gaal faces an anxious wait to discover whether he will be without his 14-goal top scorer for any or all of United's remaining four fixtures.
"Yes, Rooney was injured," he said in a news conference. "He had a shot on his knee, so we have to wait and see how heavy [serious] it is."
Van Gaal substituted the other former Everton player in the United team, Marouane Fellaini, at half-time and confirmed it was because he feared the midfielder, who was cautioned in the 11th minute, would be sent off.
"He was booked and I found that the players of Everton provoked him and I was not so sure if he should end the match," the Dutchman explained.
"That is a reason, but also because of the result at half-time and of course I could have changed more players."
James McCarthy, John Stones and Kevin Mirallas scored the goals for Everton, whose manager Roberto Martinez was particularly pleased for the centre-back after he opened his account for the club.
"John deserves his moment because scoring his first goal is a memory he is going to treasure," the Spaniard said in his news conference.
"The boys were giving him a hard time because he only scores in training. His defensive display was his best since he was playing in the first team.
" At 20 the way he defended against Wayne Rooney, Radamel Falcao and Marouane Fellaini was incredible."