The England global was taken out of the pitch after failing to overcome a nagging knock during the Red Devils 1-0 win over Wolverhampton Wanderers in their FA Cup third-round replay.
He clutched his back as he left the field before heading straight for the tunnel, and United now face an anxious wait to discover whether their 19-goal top-scorer will be fit to face the runaway Premier League leaders.
"It backfired. You have got to take them [risks] once in a while". I think he got a knock, a knee or something, in his back, but he's been struggling for a little while.
Mata scored the victor of United in the 67th minute of the repeat of the third round of the FA Cup to establish a clash against Watford or Tranmere.
Juan Mata supplied the game's only goal that will put the Red Devils toe-to-toe with third-tier Shrewsbury Town on the 26th.
And, while Solskjaer offered no update on talks to sign Bruno Fernandes from Sporting Lisbon, he said the performances of several youngsters convinced him the squad does not need a major overhaul.
"But that's been more when he's been exhausted".
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"The only thing is if Paul Pogba has decided that he wants to leave then there's not a lot you can do about that if you've got an unhappy player".
Last season only four players - Eden Hazard, Wilfried Zaha, Nathan Redmond and Raheem Sterling - completed more dribbles than Salah's 81, but in this campaign it's a different story.
"I think Mason will have a top and long career".
Rashford has featured in 13 matches - starting 11 of them - since the beginning of December, scoring nine goals in that period.
"We'll look to take the positives and build that momentum against a Southampton team that's had a bit of resurgence recently".
Williams is confident in our ability to progress no matter who we come up against, although attention will now turn immediately to Liverpool at Anfield on Sunday.
Though there is no doubting who is by far the superior side, for much of their encounter at Old Trafford earlier this season, Solskjaer seemed to have got the better of his counterpart again.