Dan Gosling will be out of action for up to nine months after picking up a knee injury at Wolves.
The 20-year old midfielder has had a scan and the diagnosis is not good.
"Our worst fears have been confirmed," physio Mick Rathbone told evertonfc.com. "Dan has ruptured his cruciate ligament and will be unfortunately be out for up to nine months."
Gosling clashed with Wolves goalkeeper Marcus Hahnemann in the closing stages at Molineux last Saturday when he was trying to grab what would have been a winning goal shortly after coming onto the field as an 83rd minute substitute.
The England Under-21 star has made a total of 17 appearances this season, scoring three goals.
"I'm really disappointed for Dan," said David Moyes. "He's been making great progress here at Everton and we look forward to having him back as soon as possible."