The Scotland international is stepping up his rehab after missing the last 13 matches of last season with a ruptured Achilles.
He told the club website: "I'm doing well, it's a slow process as we are making sure the foundations are right as you have to make sure the ankle is strong before I put full weight on it.
"My ankle gets stiff in the morning and the evening, but that is normal because there has been a big trauma. Once I get going on it then it's all right. I am walking normally now.
"I'm happy with how it's going and I hope to get some minutes on the pitch in August, but the main aim is to be fully fit by the end of September. Anything earlier is a bonus."