Burnley defender Michael Duff has been ruled out for between four to six weeks with a medial ligament strain.
The long-serving centre-back, 33, suffered the knee injury during the Clarets' Carling Cup win against Barnet.
Duff missed Saturday's 2-1 win at Derby and boss Eddie Howe told BBC Radio Lancashire: "It's another injury blow for us because he had come in and performed very well."
He added: "It makes it even more disappointing."
Burnley have signed six players this summer but Howe added: "I'm hoping to bring in a couple of players, minimum.
"That's the target. It's what I feel we need.
"Anymore than that and it would be great but I think two players minimum."
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