The Reading midfielder has been forced to undergo surgery on the knee problem which has kept him out since September 19.
Reading manager Steve Clarke said: “Stephen won’t be with us probably until end of December or January.
“He’s had an operation that we were hoping we could avoid.
“But he’s had to go in and have surgery and we’re now looking at maybe 10 weeks from now until he’s back.
“It’s a blow for Stephen. But he’ll work diligently on his rehab and get himself ready.
“His wife is also expecting a baby any day now so he’s going to be busy these next few weeks.”