Coventry defender Gary Borrowdale faces up to six weeks on the sidelines after scans showed he ruptured ankle ligaments during the midweek defeat to Watford.
The left-back, an ever-present so far this season, had to be stretchered off after just 26 minutes of the Sky Blues' 3-0 loss at the Ricoh Arena.
Manager Iain Dowie told the club's official website: "Gary felt his ankle go after a tackle but tried to carry on for five minutes before he had to come off.
"He has ruptured ligaments and that usually takes four to six weeks to recover from."
Borrowdale was not the only casualty from Tuesday evening for the Sky Blues as midfielder Stephen Hughes suffered a depressed fracture of the cheekbone.
Hughes is now a major doubt for Saturday's game against Colchester, although he could play wearing a specially designed mask similar to the one worn recently by England captain John Terry.