Ole Gunnar Solskjaer expects to be without David De Gea against high-flying West Ham as Manchester United look to stay second ahead of the international break.
The 30-year-old was allowed to return to Spain last week for the birth of his child, leading him to miss matches against Crystal Palace, Manchester City and AC Milan.
Solskjaer has confirmed De Gea is back in England ahead of Sunday's Premier League clash with the Hammers and said the goalkeeper was "touch and go" to start at Old Trafford.
Travellers from Spain are currently able to be released from quarantine if they test negative for Covid-19 after five days of isolation – a timescale the United boss now believes will probably rule the number one out.
"David is probably released from his quarantine and isolation with a test on Sunday afternoon maybe," Solskjaer said in an update on Saturday. "So he probably won't make this game."
De Gea's continued absence would see Dean Henderson start a fourth straight match for United, just days after he failed to keep out Milan defender Simon Kjaer's header in a potentially costly 1-1 Europa League draw.
That last-gasp goal give Stefano Pioli's men the upper hand heading into Thursday's last-16 second leg, which is followed by next Sunday's FA Cup quarter-final at Leicester and the international break.
It is shaping up to be a key week and Solskjaer stressed the importance of getting a positive result against David Moyes' impressive Hammers in their final Premier League fixture of the month.
"I think they've been brilliant," said Solskjaer, who oversaw a superb 2-0 win at runaway Premier League leaders Manchester City last weekend.
"We played them in the FA Cup not so long ago as well. We went to extra time. It was a tight, even game.
"He's got players who score goals, they are creative, they defend really well. They're really difficult at set plays.
"David's done a tremendous job that we know he is capable of, so I am very happy for him.
"We know this is a big game for us. It's maybe too far ahead to City so of course we need to consolidate our place in the top two or three hopefully."
Marcus Rashford is a doubt and Anthony Martial needs assessing after a hip issue forced him off on Thursday, when his half-time replacement made an impressive impact.
Amad Diallo marked his third substitute appearance with a superb improvised headed goal, leading to praise from Solskjaer for the 18-year-old winger signed from Atalanta in January.
"Of course it's a big change for him," the United boss said. "He's moved over here by himself
"But he is coming into training every day, he's working really hard. He knows he has a lot to learn.
"He's an exciting talent, of course, but he'll have to get used to the tempo and the quality of the level he's playing at now.
"He didn't play too much for Atalanta either, so we've been gradually giving him more and more. But he's been hungry to learn and his appetite in training has been spot on."