Everton manager David Moyes says defender Phil Jagielka could be missing for up to six weeks after damaging medial ligaments in his right knee in the Premier League loss to Bolton.
The England international limped off in the first half of Everton's 2-1 defeat on Wednesday and left Goodison Park on crutches.
Moyes said Friday "to lose him is a massive blow to us because he is an integral part of the defense and very important to us."
Jagielka could miss as many as six Premier League matches but should be fit to return in time for England's friendly against the Netherlands on February 29.
Everton are 11th in the 20-team standings.