The 21-year-old, who spent the 2013-14 season on loan from Barcelona, suffered a hamstring injury in the Asia Trophy in Singapore a fortnight ago.
"He's already working at 60 percent so I don't expect him to be too far away," Martinez told reporters.
"Maybe the weekend will be too early for him."
Everton also have doubts about another winger, Kevin Mirallas, and the England defender John Stones for Saturday's opener after both were injured in Sunday's testimonial match for former striker Duncan Ferguson against Villareal.
Mirallas will be assessed by medical staff tomorrow.
The 21-year-old has had problems with hamstring injuries before, missing two months of his loan season at Goodison after being stretchered off at home to Fulham in December.
(Reporting by Steve Tongue; editing by Martyn Herman)
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