Adam Matthews will miss Bristol City's Severnside derby against his old club Cardiff at Ashton Gate (kick-off 12pm).
The Sunderland loanee could be sidelined for anything between two and 12 weeks with a problem that stems from his ligaments between the hamstring and calf.
Korey Smith also sits out the Sky Bet Championship game after being ruled out for at least a month with a hamstring injury.
Hordur Magnusson (hamstring) and Frank Fielding (groin) could be fit, but Gary O'Neil is now suffering from a sickness bug after overcoming a nagging calf problem.
Cardiff are set to welcome back key players rested for last weekend's FA Cup defeat to Fulham.
Aron Gunnarsson is back from a short break in Dubai, which Bluebirds boss Neil Warnock felt was necessary following the Iceland midfielder's schedule on the back of his Euro 2016 exertions last summer.
Kenneth Zohore and Peter Whittingham are in contention after minor knocks, the latter having marked his 10th anniversary as a Cardiff player in midweek.
Lee Peltier should also return at right-back in place of Jazz Richards after missing the Fulham game with an ankle problem.