Manchester United's top scorer Marcus Rashford could be out for at least six weeks with a stress fracture, according to manager Ole Gunnar Solskjaer.
The England international went off 15 minutes after coming on as a substitute in Wednesday's 1-0 FA Cup win against Wolves after picking up a knock.
Rashford was not included in the squad for Sunday's trip to Premier League leaders Liverpool.
"Normally six weeks to heal, but I'm not a doctor," said Solskjaer.
"It's a [back] stress fracture. It happened against Wolves. It's not happened before, it happened there and then. He'll be out for a while."
He added: "We will give him enough time to heal, normally six weeks before getting going, then he needs time to get match fit again."
When asked whether the club would seek a replacement for the 22-year-old, the Norwegian added: "We've had many injuries for big players this season. It's just an unfortunate situation we're in.
"We might look at some short-term deals as well that could take us through to the summer. We don't desperately need a striker, if the right one is there and it fits for us... we've got players who are champing at the bit."
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Rashford has scored 22 goals for club and country this season, with 14 of those coming in the Premier League.
On Monday, Rashford tweeted: "On the pitch or not, Manchester United fans don't get much bigger than me.
"You best believe I'll be involved in team meetings, team huddles and team sessions throughout this recovery. Blink and I'll be back, fitter than ever. See you soon."