Gylfi Sigurdsson is expected to be sidelined for six to eight weeks with a knee injury after seeing a specialist, Everton have announced.
Sigurdsson picked up the injury in Saturday's Premier League victory over Brighton and saw a specialist on Monday evening.
The timeframe means the 28-year-old is likely to miss the rest of the Premier League campaign.
"We'll continue to assess Gylfi's progress on a week-to-week basis and the medical team will work very closely with him, as they would with any injured player, to get him back playing as quickly as possible," Everton manager Sam Allardyce said.
Provided he does not suffer any setbacks, Sigurdsson should have enough time to recover fully for Iceland's opening World Cup match against Argentina on June 16.
Sigurdsson has had a mixed first campaign in a difficult season at Goodison Park but has grown in influence under the management of Sam Allardyce and has scored seven goals.