Leicester City defender Aleksandar Tunchev could be sidelined for a further six months.
The Bulgaria international was ruled out for the rest of the season in January.
But after an unsuccessful course of injections he has had to have another operation and could now struggle to be fit for the start of next season.
"He had a scan on Tuesday and had an operation on Wednesday, so we are looking at the start of next season now to get him back," said manager Nigel Pearson.
"He has had the microfracture operation and the recovery is four to six months, and he will be ready for the start of next season."
Meanwhile, Pearson is hoping that striker Matty Fryatt will soon be back from injury after he broke his jaw at the start of February.
"It will be four weeks on Tuesday, so we will find out then," said Pearson.
"His jaw will have been wired up for four weeks and then it will be a case of reassessing where he is at, whether that be with a scan or an X-ray.
"Then there will be a decision taken on whether any further work needs to be done.
"Hopefully, because he has been at home for four weeks and the injury has been stabilised, we will let nature take its course.
"It is the same time scale as before and we are looking at eight weeks, hopefully, if things go to plan."