The 34-year-old suffered the problem during Saturday's goaless freidnly draw with Hadjuk Split, his only involvement in the club's tour of Croatia and Slovenia.
"It is frustrating because I have got a bit of a hamstring niggle so I have not been able to do much training but hopefully that will clear up pretty soon and I can get back to training," he said.
"The training sessions are coming thick and fast but that is pre-season for you and the hamstring strain is nothing too serious - I can still do the running, just not the ball work.
"So I am still feeling really fit and I just want to get some games under my belt, like I think we all do now."