Everton defender Phil Jagielka may not play again until after Christmas after undergoing a second knee operation.
Jagielka, 27, has been sidelined since damaging knee ligaments in April but had pencilled in a return to action at the end of November.
However, he has now suffered a setback, described by Everton as "a small cartilage tear", which means his return has been put on hold.
Everton boss David Moyes has confirmed that the England international had an operation on Wednesday.
"Jagielka had an operation on a tear in his meniscus, which is the cartilage in his knee," he told the club's official website.
"We think [it has set him back] four to six weeks. He was down initially but he's on the road to recovery now."
Victor Anichebe has also suffered a complication in his recovery from a knee injury.
He has not played since February and the 21-year-old appears some way off a return to the first team.
Moyes added: "Victor's not in a good way either. He had the pin taken out four to six weeks ago which had been catching on the side of his knee.
"Now what has happened (is that) he has a massive growth of bone and has a really big knee at the moment. We don't know how long it will be."
Such ill-fortune has plagued Everton's season but Moyes insists his club's run of seven games without a win has little to do with bad luck.
Moyes takes the Toffees to West Ham on Sunday for a Premier League game critical to both sides, who are sitting just above the relegation zone.
Moyes is hoping to have striker Louis Saha back from a calf injury, on the ground where he scored two sensational late goals last season to produce a shock 3-1 victory for Everton, who had been trailing for much of the match.
The Scot said: "We have had bad luck, but not all the time. We have to decide when it's luck and not just bad play.
"But we know we need to do better, and not rely on such things as luck.
"There has been signs that we are getting better throughout, but not enough to get us back to where we want to be.
"It can be about confidence, but that can change very quickly. We certainly need to get that back.
"But there is no need to think in terms of rebuilding confidence, it is not like that. A few of the lads are doing okay, but we need to play better as a team."