Man Utd are concerned Paul Pogba will be sidelined for a further two weeks longer than initially expected with his current thigh injury.
The Frenchman has missed United's last two fixtures due to the problem and could be ruled out of at least three more.
According to the Mail, Pogba is almost certain to be ruled out of both legs of United's Europa League last-32 tie with Real Sociedad, starting this week.
He will also be sidelined for next Sunday's clash against Newcastle, while his return for the following weekend's meeting at Chelsea is not guaranteed.
United are not putting a timeframe on his recovery, but will be hopeful of Pogba playing some part in the match at Stamford Bridge.
Chelsea's presence in the top four again has added extra importance to that fixture, while United then face rivals Man City six days later.
Pogba's absence has already been felt since he hobbled out of action in the game against Everton.
It took extra time for United to find a way past West Ham in the FA Cup, and they looked sluggish in their draw with relegation battlers West Brom on Sunday.
Solskjaer said before the game at the Hawthorns: "We’ve done well without Paul but of course he’s been really good lately so we hope to get him back as soon as we can."
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United's prospects of mounting a title challenge are now hanging in the balance, and Pogba's involvement in the Chelsea and City fixtures will be crucial to their chances.
But despite dropping two more points at the weekend, Solskjaer insists his team are in it for the long haul.
"I said with 15 games to go we shouldn't be talked about at this stage," he said. "It's a compliment for the boys that we got into the position we are now.
"We won't let them (City) run away with it. We're playing them soon, and we're not giving it away early. This season is so unpredictable, of course we aren't going to settle for second."
