The injury kept McCombe out for part of last season, although the centre-half did feature in the run-in and the final game of the campaign at Brentford when Rovers won the League One title so dramatically.
He suffered a setback over the summer but is back on track to make a return to action early in 2014.
Doncaster physio Alex Dalton told the club's official website: "He is on target but will be around four months before he can start playing again.
"At the moment he is only doing light work due to the brace. He will be doing light bike work and arm weights during the period as we continue to assess his progress."