The Scotland international scored twice in the opening six games of the season before suffering the injury. He made a comeback in January but lasted only two games before deciding to go to America for an operation.
Caretaker manager Frank Barlow confirmed: "Our medical staff have already reported an improvement in Scott's condition but realistically speaking, he's looking to get himself ready for next season.
"It's been frustrating but hopefully he can now see an end to his problem."
Former City Ground midfielder Scott Gemmill has left Oxford United after just two weeks with the club.
The 35-year-old had teamed up with Jim Smith in a player/coach role but has been offered a deal to continue his career in New Zealand.
Roy Keane meanwhile may not get a Scottish League title medal as he has not played enough games for Celtic following his move from Manchester United.
The former Forest man needs to feature in four more games but is currently injured. Celtic can appeal to the SPL if Keane does not qualify automatically.