Leicester defender Patrick Kisnorbo faces up to six months out with a partial anterior cruciate ligament tear.
A scan has revealed the extent of the damage and the 27-year-old will require surgery over the summer.
"It looked innocuous at the time, but those cruciate injuries always do," City boss Ian Holloway told the club's official website.
"We have now got to decide if he will have his surgery over here or in Australia.
"The good thing is he has got the right people around him at the club. Our medical team here have dealt with similar injuries in recent years and they are confident that he will come through it.
"Levi Porter did his cruciate against Chelsea earlier in the season and he is back in training now."
