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Burnley forward Jacob Bruun Larsen has been ruled out for up to three months with a stress fracture.
The 28-year-old Denmark international has scored twice in nine Championship appearances this season.
Boss Nicky Hayen also revealed veteran striker Jamie Vardy, 39, will not make Saturday's trip to Lincoln with a back injury, although midfielder Josh Cullen could be in the squad after missing the past 10 months with an anterior cruciate ligament injury.
The Clarets are 22nd in the table after winning just one of their opening 11 league games of the season.
"We have nine injuries that if you have them in the selection you have a lot of solutions but for the moment they are not available," Hayen told BBC Radio Lancashire.
"That's really unfortunate but that's the solution for now."
The Clarets fell to a 2-1 home defeat by Wolves last week after Vardy had given them the lead and are without a win in front of their own fans since a 2-0 victory over Leeds in the Premier League on 18 October 2025.
If Burnley fail to beat Portsmouth in their next match in front of their own fans on Saturday, 31 October they will set an EFL record for the longest spell between home wins.
Hayen, who took over in the summer, said he understood why fans were "angry" at the side's dreadful form.
"I understand that the fans are unhappy but in a human way it hurts for me also," he added.
"I want to make them proud and do everything to be successful for them. As a human being it hurts but as a professional coach you have to accept that they are angry.
"We try to do the best that we can but if we have these nine players available for selection everything changes because you have much more options that you can use during the game.
"Now we have players that we have to bring on because we don't have anyone else."