Scans on the hamstring injury the teenager sustained in Saturday's 4-1 win over Fulham suggest the forward will be out for up to five weeks.
On Monday the club confirmed the 19-year-old would be sidelined for some time but Martinez has been more specific on the timeframe to get Deulofeu back.
"It was confirmed that Gerard has suffered a soft tissue injury in his right hamstring," the Toffees boss said.
"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 under-estimated."
Deulofeu is on a season-long loan from the Catalans and will return to his parent club later this week so they can also assess the extent of the injury.
Martinez said Everton would be liaising with Barcelona over the player's rehabilitation.
"We're working with the two medical departments," he told evertontv.
"They're working together because, as you can imagine, there are many things to take into consideration and it's important they have a look as well.
"From there, we're going to use the best possible route to treat the player.
"Gerard has got a good feeling about him and all he wants is to get back as quick as he can.
"I think this is going to refresh him and it's going to make him a real impact player when he comes back, so we're excited about that."