"I had an arthroscopy two weeks ago. The target was to wash out some pieces of cartilage that were loose in the joint. My knee had swollen and the movement was being blocked every time I ran, so we had to do something," he told the clubs official website on Thursday.
"Everything went well so now I just need to recover my strength, especially in my thigh muscles. But the knee feels very good. I'm at the stage now of slowly building up the work that I do on the leg.
"I would hope that I would be available for selection again by the end of the month - I think the Portsmouth game is a bit too early for me unfortunately.
"I started to feel it at the beginning of the season, but I was able to manage for a while. It was getting worse though and we really had no choice about doing the operation now if I wanted to be 100 per cent fit."