Erling Haaland is set to miss the next few weeks after suffering a hip flexor injury.
Borussia Dortmund manager Marco Rose confirmed that he will be without the Norwegian striker for several games.
Haaland played the full 90 minutes of Dortmund's Champions League defeat to Ajax but could now be absent for the reverse fixture, which takes place on November 3.
United want Leipzig pair Nkunku and Haidara - Paper Round
The 21-year-old tweeted: "Time to focus on my recovery. I'll be back stronger."
Haaland had only recently returned from a muscular problem that had left him unable to walk at the start of the month and caused him to miss Norway's October internationals.
While Rose would not speculate on the nature of the injury, it is thought that it may be a recurrence of the previous problem.
"This is not good for us and not nice for [Haaland]," Rose said ahead of his side's Bundesliga encounter with Arminia Bielefeld.
Erling was really down yesterday. He was happy that he was back. He had no problems after the game against Mainz.
"We are very thin in attack now."
Haaland scored twice on his return against Mainz but had been quiet in the 4-0 thrashing by Ajax.
Ten Hag and Rose on 'deserved victory' for Ajax against Dortmund
Thomas Meunier (foot) and Nico Schulz (torn muscle) are also on the injury list for Rose, whose side are second in the Bundesliga behind Bayern Munich.
"This is the chance for the guys who come in to perform and draw attention to themselves," says Rose.
Pedri wins 2021 Golden Boy award, Bellingham second
Opinion: Ballon d'Or could lose relevance in post-Messi/Ronaldo era, and that's a good thing