The 29-year-old had an operation three weeks ago and is now recovering well under the guidance of physio Jon Whitney.
"Stephen's rehab is going well," Whitney told the club's website. "After the surgery he rested up for a fortnight before starting his rehabilitation course last week. We have been working on his core strength and fitness and he has responded well.
"We are building up to running and we're aiming for Stephen to return to full training with the rest of the lads at some point during our pre-season schedule.
"He is making good progress."