The Scotland international has managed just 27 minutes of first-team football since joining the Lilywhites from Leicester City in the summer because of the problem.
The latest scan on his calf showed that the problem has healed, but he is still unable to sprint without pain.
Preston’s medical staff believe this is due to an imbalance in his ankle caused by a serious injury he suffered earlier in his career.
They are though confident that the problem will not rule him out long term and expect him to resume full training in two to three weeks’ time.