Roberto Martinez has described Leighton Baines's latest injury setback as "a real disaster" for Everton.
The defender underwent surgery on his ankle in May before returning to action in pre-season, but he aggravated the problem in training, forcing him to miss the 2-2 draw with Watford on the opening day of the new season.
"We don't know how long he will be out for, but it has been a real disaster," the manager is quoted as saying by BBC Sport.
"We were preparing for the Watford game and in training, he blocks the ball and it hits him in exactly the same place where he had surgery.
"It was devastating, because he had worked so hard and looked stronger than ever. I don't think I had seen him looking as powerful and refreshed in the last two seasons. Then there was this big knock."
Baines, who joined Everton from Wigan Athletic in 2007, made 38 appearances in all competitions for the Toffees last season.
