The Barcelona loanee has been ruled out until the New Year after pulling his hamstring in the Toffees' win over Fulham, meaning he will miss the club's next seven matches
The Spain Under-21 winger was taken off on a stretcher after pulling up in the second half of Everton's 4-1 win over Fulham on Saturday afternoon.
And, after the club had only disclosed that the youngster would miss “a few weeks”, Martinez has now revealed the full extent of his injury and believes he will be sidelined until the New Year, with five weeks of recovery needed before he can make a return.
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“Obviously we now need to make sure he recovers well. We don't think he's going to be out for too long, probably the best part of five weeks. But, knowing Gerard, he's a sprinter and we need to make sure he's fully fit.
“Gerard is happy. Obviously he was disappointed, but we were probably a little bit fearful that it could have been a bit more than [it is], so we're pleased that it's an injury that we know exactly what it is and that it's not going to bring any more problems in the future.
“But we need to treat it right because those sorts of injuries cannot be underestimated.”
The Barcelona loanee is therefore likely to miss seven games for the Toffees over the busy festive period, though could make his return to action against Liverpool on January 28.
Deulofeu had been beginning to push for a permanent place in the Everton first team before suffering the injury, scoring a late equaliser against Arsenal after a man-of-the-match display against Stoke before that.
The youngster has impressed at Goodison Park after being handed a larger role, and Martinez recently revealed that the club have the opportunity to keep him on loan for the 2014-15 season too.