The City centre-back has been sidelined for the past two months with a knee injury and Johnson has resigned himself to being without McCombe's services for the remainder of the campaign.
"We won't see Jamie this season. It's a bad situation because he's a big club in our bag,2 the City boss told the club's official website.
"It will take him a little while to get over the scope camera he had in his knee and the specialist feels he needs a complete break to clear up whatever is in there.
"We can't think about him until the end of the season, if we get him back a bit earlier fantastic but I think he's out until the end of the season."