Derby County midfielder John Eustace will miss the rest of the season after undergoing a second knee operation.
The 35-year-old had initial surgery in January, and last played in a 1-0 win against Ipswich Town the same month.
First-team coach Paul Simpson said: "We are looking at rehab time probably being 12 weeks, so we don't expect John to be available again this season."
But George Thorne and Jake Buxton could be back in time for the final Championship game of the season.
Injuries have restricted midfielder Thorne, 22, to just three appearances this season, but he could return from a thigh problem in time for the home game against Reading.
Centre-half Buxton, 30, has missed the last seven matches following back surgery.
Simpson added: "We are hopeful George and Jake could be back for the Reading game. That is with fingers crossed, hoping everything goes to plan."
Eustace began a second spell at Derby in the summer of 2013 and has made 14 appearances this season.