Ole Gunnar Solskjaer plans to sign a loan forward after confirming that Marcus Rashford has suffered a double stress fracture of his back.
Manchester United have been rocked by the loss of their top scorer for up to three months.
Solskjaer, who lost Erling Braut Haaland this month, now faces a desperate search for reinforcements as negotiations on January’s main goal Bruno Fernandes have stopped.
The United manager said: “We have had many, many injuries this season, it is an unfortunate situation.
“The window is open, so we could look into some short-term offers to get us through the summer.”
Solskjaer made the acquisition of at least one forward a priority over the next two windows.
But he had to go back to the drawing board after seeing Haaland head for Borussia Dortmund.
The Norwegian stressed his potential with a hat-trick in his debut for the Germans.
He also wants to shelter on the right, with Jadon Sancho a main target – but accepts that he won’t be able to get the names on top of his wish list before summer.
Rashford is ready for non-invasive surgery to repair his back and will not be able to resume training for at least six weeks.
His injury means that United is desperately running out of bodies, with Scott McTominay and Paul Pogba also sidelined for a long time.
Solskjaer added: “The players are giving absolutely everything. When Scott, Paul, Marcus are missing, any club and any team will notice. So this could mean that we could look into some short-term offers to take us to summer.
“The permanent signatures we are looking for, the goals will not change because we have injured two or three players in the coming months. He has yet to have a plan behind them.
“But there may be short-term deals we have to make.”
As he hopes to take cover, Solskjaer admits that United will have to rely on 18-year-old Mason Greenwood in the absence of Rashford.
“We just have to do it for a while,” he added. “It has been absolutely fantastic all season.
“We’ve had a similar spell with Anthony out for eight weeks and Mason has had a few games and now has some more. Juan (Mata) is returning to his best, so we’ll just have to face it.
“We have been careful with him (Greenwood) because he is the best player and this is a possibility for him. But it could be that we do one or two things in the window.”