The Wales international first sustained the injury last season but he had made a successful return to training and played in three Under-21 games for the club as he continued his comeback.
However, he began to feel discomfort in his knee during a routine goalkeeping session this week and tests revealed that he required a second operation.
Goalkeeping coach Pat Mountain told the club's official website: "It wasn't even the heaviest of sessions that we do. He has done far more physical work since he came back.
"He just felt something wasn't right with the knee and it suddenly felt sore so he went straight in to be checked out.
"When the scan results were known on Tuesday everyone concerned was just gutted for him but we will all be there to help him get straight back on the road to recovery."
The 25-year-old has made 152 league appearances for Wolves.