Aleksandar Tunchev out for six months
The Bulgarian international had received a course of injections in Spain last month in a bid to avoid surgery, but he was forced to go under the knife and is now battling to be fit for the start of next season.
Earlier this season, the 28-year-old had made a comeback from an anterior knee ligament he received in the FA Cup at Crystal Palace in January 2009, which had ruled him out of the second half of the League One title campaign.
However, after making three appearances, he damaged his knee again against Preston North End and had to undergo further surgery in September.
The problem, which is not related to the original ligament tear and involves the cartilage in the joint, has persisted and he flew to Barcelona last month to receive the injections from the surgeon who conducted his original operation.
However, the treatment has been unsuccessful and he has had to undergo a procedure called microfractures, which involves drilling small holes in the bone to cause a bleed, which then calcifies to form new cartilage.
"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, striker Matty Fryatt will discover on Tuesday whether he will need further treatment on his broken jaw.
City's top scorer broke his jaw in two places in the 0-0 draw with Doncaster Rovers on February 9 and had to undergo surgery.
Having his jaw wired, the 23-year-old was told to rest at home for four weeks to let the injury settle down before having another scan to determine how successfully it had healed.
Pearson is hoping to have Fryatt back by the end of the season and possibly in time for the play-offs if City finish in the top six.
"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."
Pearson has no other injury concerns ahead of tomorrow's trip to Sheffield Wednesday.
Blackpool boss Ian Holloway believes Daniel Nardiello will benefit from his spell at League One strugglers Oldham.
Nardiello has joined the Latics on loan until the end of the season after finding first-team opportunities hard to come by.
Holloway said: "Dan needs to be playing regular first-team football at a decent level."
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