The 19-year-old, who scored in the League Cup this week, is currently on loan from Barcelona.
The Toffees boss admits that a permanent deal is unlikely, but reveals that Everton could keep the Spaniard beyond this season.
"We can take him for a longer period," Martinez told reporters. "I don't think it's an option to take him permanently because the hopes in Barcelona are huge for him, but with him being such a young man, perhaps we could extend for a further year.
"The deal is performance based, so depending on how many games he plays, financially there is a difference. It decreases if he plays more."
Everton take on Cardiff City in the Premier League this afternoon.