Rojo has been sidelined since April with the problem, but travelled with the squad on their pre-season tour of the United States and featured in their open training session ahead of their Champions League clash with Basel in midweek.
Mourinho confirmed that the Argentine is still some way from being available again, but hinted that he may be back before the end of the year.
"Marcos Rojo is still in the timings after such an important injury. Everything went really well, but he is not even training with the group in a normal session, he's just doing parts of it," he told reporters.
"So I think Marcos has in front of him probably has a couple of months."