"He isn't as far forward as we thought he would be. He is a few weeks away," says the United boss.
"With this injury it is a long remedial period and he did a lot of hard work so we decided to give him a break. He went off for a holiday with his family.
"He needed a break because he can sometimes push himself a bit hard. He is back and he was out doing some good work on Friday morning but I think he is a few weeks away from playing.
"I wouldn't say it's a good thing that Roy won't be available to us for the City game, not at all. I would have loved to have him in my team next Saturday."
Keano’s ban starts on Tuesday against Leicester.
Injuries are spreading to the youngsters too:
Danny Byrne has undergone cruciate ligament surgery after he was injured playing for Ireland Youth, and Darren Fletcher is out of action once more with a stress fracture in his foot.
To cap this, Danny Webber has had his loan period at Watford cut short after fracturing his shoulder.