The talented 21-year-old winger joined the Toffees from the Catalan giants for £4.2million in the summer but the complexity of the deal allows Barca to purchase him in any of the next two summer windows.
The reigning Spanish champions are able to activate a buy-back clause of £6.3m this coming summer, or £8.4m in the 2017 window, which Everton can do nothing about according to Martinez.
"There is nothing we can do if they activate it," said Martinez.
"That was the deal and the only way we could access the player on the terms that we wanted. I'm delighted with the deal.