The Toffees announced on Saturday ahead of their 2015-16 Barclays Premier League opener against Watford that Baines would miss the game having sustained the problem.
A statement from the club revealed the knock is to the ankle on which the 30-year-old had surgery in May, a procedure that forced him to miss the final two matches of last season.
And while Everton would not give an estimate as to the amount of time Baines might be out for, it is understood there are fears it could be a significant duration.
Everton boss Roberto Martinez said on the club's official website: "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.
"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."
Source : PA
Source: PA