David Moyes has admitted his fears for Jack Rodwell after his third hamstring injury in as many months.
The 20-year-old has played just over 100 minutes in Everton's Premier League campaign since picking up his first two England caps against Sweden and Spain in November.
Rodwell looked like he was back in contention for Moyes' first-team plans after training with the squad on Monday, however the midfielder complained of tightness in his hamstring on Friday and was immediately sent for scans.
With Chelsea on the horizon, Moyes has revealed Rodwell's latest setback means he will again be out of action.
"We have done everything we have thought we needed to do but it looks like he will be out of action," the Scotsman told the Daily Mail.
"It is a big concern. We had given him longer to recover from this injury than we should. He has done lots of extra work, lots of strengthening.
"I was looking forward to having him back because we need him. We need that freshness. He was certainly in contention to start, that's for sure.
"We are having to check whether it is something in his nervous system or something in his back. In truth, at this moment, I don't know."
Rodwell, a reported Manchester United target, first sustained the injury during the warm-up against Norwich in December.
He came back within two weeks but after coming on as a substitute against Bolton last month, the young England star aggravated the problem which has left him sidelined ever since.