Ole Gunnar Solskjaer fears Marcus Rashford will be ‘out for a while’ with a groin injury.
It means the Red Devils do not have a recognised striker available ahead of Wednesday’s Carabao Cup clash against Rochdale with Mason Greenwood (illness) and Anthony Martial (thigh) currently sidelined.
Solskjaer said: “He [Rashford] will have a scan tomorrow. He felt his groin. I think he will be out for a while. I can update you later when I know a little more.
“It is just one of these moments, we’ve had historically loads of centre-backs the last few years struggling with injuries when we’ve come here.
“[Michael] Carrick played centre-back, Darren Fletcher played, at the moment it is strikers.
“Hopefully Mason and Anthony will be back for definitely Arsenal, and hopefully one for Rochdale.”
Goals from Andriy Yarmolenko and Aaron Cresswell condemned United to a second Premier League loss of the season.
Solskjaer has won just five of his last 19 games in charge, but reminded United fans to be patient.
He told talkSPORT: “I’ve said it many times, this is a rebuilding job and the boys are working as hard as they can.
“Behind the scenes we’re working and we want to improve and I wouldn’t be anywhere else with anyone else.
“They’re tight, even games and sometimes there’s not an easy explanation why you don’t get results.
“Like today, it could have easily gone our way, but it did their way. We’ve just got to work to tip it our way.”