Sir Bobby was quick to play down the seriousness of the injury.
"Cort reported to the training ground earlier in the day with a badly swollen knee,” he said.
"There was fluid there and we're not quite sure why. It's possible he did some damage in the weights room but we don't think it's a serious injury.
"We pulled him out of the reserves as a precaution and we'll assess him again before the end of the week.
"It's a shame for Carl but it's not a bad one."