Middlesbrough striker Jeremie Aliadiere has aggravated his hamstring injury.
"I had been running and sprinting and going well but I have been feeling some discomfort in training this week so I will have to take it easy," Aliadiere told the Northern Echo.
"I don't want to damage it again so it may be another week or so before I can start training. I don't think I have a chance of facing Chelsea.
"I am now looking at playing Manchester United a week later if I can. It's been very difficult for me.
"I'm disappointed because I have been feeling good in training and I'm a bit down about things now. I just want to be playing again."