Sheffield Wednesday striker Steven MacLean has been ruled out for at least four weeks.
The 23-year-old injured his knee in last Saturday's 1-1 draw with Burnley, but boss Paul Sturrock had been hoping to have him back within a week or two.
The extent of the damage was more serious than initially thought though, and MacLean is now set to undergo an exploratory operation.
"The X-ray has shown a bit of inflammation in the knee, around the area he had his last injury," Sturrock told Wednesday's official website.
"If we rest it for three to four weeks, then find it needs an operation, it would take him seven to 10 weeks.
"The consensus of opinion is we do an exploratory operation on him now, which again is four weeks minimum."
MacLean's injury leaves The Owls without a fit senior striker for the game against Plymouth on Saturday, with Marcus Tudgay (toe), Drew Talbot (knee), Deon Burton (hamstring) and Barry Corr (thigh) all sidelined.
Sturrock is likely to be forced into the transfer market in order to bring in some emergency cover up front.