Henrikh Mkhitaryan limped off with an apparent leg injury in Manchester United's Europa League round-of-32 second-leg clash with St Etienne on Wednesday.
The United midfielder gave Jose Mourinho's side a 1-0 lead with a near-post finish just after the quarter-hour mark, but came off in the 25th minute holding the back of his right leg.
The Armenia international was replaced by Marcus Rashford and is now a doubt for Sunday's EFL final clash with Southampton.
Mkhitaryan, who joined the club last summer from Borussia Dortmund, has scored five goals and provided a further five assists in 23 matches this season.