Everton boss Roberto Martinez fears that Leighton Baines could be facing an extended spell on the sidelines after it was confirmed that the defender would miss the season opener with an ankle injury.

The England left-back underwent ankle surgery in May and missed a large chunk of Everton's fixtures this summer, but he had said that he was pleased to return to action after featuring against Hearts a fortnight ago.

However, the 30-year-old has suffered another setback and Martinez admitted that he is worried about the extent of the problem.

"With Leighton, it was a very, very unfortunate block in training where the ball hit his ankle that he had a little bit of trouble with in the later stages of last season," Martinez told reporters.

"It's really sad and disappointing because Leighton came back probably stronger than ever and this pre-season he showed fantastic signs. So to lose him in the week that you're preparing to start the season is very disappointing.

"We're just hoping we can get him back quicker than we fear because the injury looks very similar to what he had before."

Everton begin their Premier League campaign by hosting newly-promoted Watford.