The 25-year-old injured his knee while running last week and faces up to eight weeks on the sidelines.
Physio Steve Allen told the club website: “Unfortunately Kieran suffered cartilage damage in his knee while doing some running two days before he was due back.
“He had a bucket-handle tear of his meniscus and underwent surgery. The surgery was a success and he’s on the road to recovery now.
“He’s going to be out for six to eight weeks. It’s a matter of getting his range of motion back and his strength back before getting him into training again.”