The Daily Mail says Loftus-Cheek has suffered another injury setback while training with Chelsea's Under 23s.
The 22-year-old England World Cup hopeful, on a season-long loan at Crystal Palace, had returned to his parent club for treatment after picking up an ankle problem in December.
He has recovered from that injury but while training with Chelsea's youngsters at Cobham on Monday felt a pain in his knee.
"Unfortunately in a training session where his ankle was being tested with the U23s and the session went very well, he has managed to pick up another very minor injury," Palace manager Roy Hodgson confirmed. "Now it has to be treated before we get him back here.
"The good news was that the injury which has kept him out for a long period of time — the ankle — that seems to be much better and he seems to be on the mend from that."