Derby County's recent revival has been hit by an injury to midfielder Stephen Pearson, who could be out of action for up to four months.
The Scotland international, 26, has had surgery on a knee problem which has troubled him since last month.
"It is a blow to Stephen and us," Derby manager Paul Jewell told the club's official website.
"He has had a problem for a while and has been playing with the help of an injection.
"The operation went very well but it is a serious injury and will probably keep him out for three to four months."