Paul Pogba left Old Trafford on crutches following Manchester United's 3-0 Champions League win over Basel on Tuesday after being forced off with a hamstring injury.
The France international, named captain for the night by manager Jose Mourinho, had to be replaced in the 19th minute by Marouane Fellaini after stretching into a challenge with Mohamed Elyounoussi, as reported by the Express.
Marouane Fellaini was only passed fit for the game on Monday after missing the 2-2 draw with Stoke on Saturday with a calf injury, but he still supplied the opening goal.
United boss Jose Mourinho was unable to give a definitive update on Pogba's injury, admitting he does not yet know the full extent of the injury before a scan on Wednesday.
"I don't know [what the severity is],'' Mourinho said. "It looks for me too [like a hamstring injury] but I haven't spoken yet to the medical department.
"We don't cry, no Paul for Sunday [against Everton], we have [Ander] Herrera, we have [Marouane] Fellaini, we have [Michael] Carrick, we have [Nemanja] Matic."
Fellaini made a promising start replacing Pogba, heading in the opening goal a quarter of an hour after replacing his injured colleague and later supplying the cross that led to Marcus Rashford, another one of Mourinho's substitutes, wrapping up a freewheeling win.
Romelu Lukaku's headed goal means he has now scored six times in as many appearances for his new club. Lukaku, is playing with sky-high confidence and Fellaini seems intent on showing he can be a productive wearer of United's colours.
United will need that to continue because Pogba's absence will be a considerable loss. The French midfielder left the stadium on crutches after the match, according to the Metro.
Jose Mourinho tore into United's star players after the 3-0 win over Basel, later complained that he was not happy with the team's attitude at 2-0 and Mkhitaryan, almost certainly, was one of the players he was talking about, as reported by the Guardian.
"Everything changed," Mourinho said. "We stopped playing seriously and stopped making right decisions. We were playing fantasy football â PlayStation football. I don't like it, flicks and tricks.
"We gambled and you have to respect your opponent. We lost position, our shape, we lost balls in easy situations.
"I didn't like it, the players relaxed too much."