Everton will be powerless to prevent Gerard Deulofeu re-signing for Barcelona next summer should the European champions activate a €9m (£6.3m) buy-back clause, Roberto Martínez has confirmed.

Deulofeu returned to Goodison Park this summer in a €6m transfer from Camp Nou having enjoyed a successful loan stay in 2013-14. The 21-year-old had found first-team opportunities understandably limited at Barcelona and also struggled to make an impact while on loan at Sevilla last season, but the Catalan club were reluctant to let the winger leave during their transfer embargo and insisted on a buy-back option lasting two years.

The winger has been in fine form recently for Everton and Spain Under-21s, scoring a hat-trick against Georgia and twice against Croatia during the international break having been named captain for the European Championship qualifiers. Deulofeu’s development is being closely monitored by Barcelona and it has been suggested that, even if the player does not feature in Luis Enrique’s first-team plans, the Spanish champions could re-sign him with a view to selling on at a profit.

But Martínez explained: “They can’t do that. There are certain things in the deal. They can’t take him back in the winter so they can’t take him back in January. It can only be at the end of the season. It is €9m for the first year and €12m in the second year.

“If they take him back they can’t sell him for a season, so he has to stay in the first-team squad for a season. At the end of that if they decide to sell him we have got first rights of getting him back or we have got a big percentage of that deal. There is nothing we can do if they activate it. That was the deal and the only way we could access the player in the terms that we wanted. I’m delighted with the deal.”

The Everton manager insisted the complex deal and risk of losing Deulofeu after only one season is offset by having a player of that talent for €6m. “My worry would be to lose him in January, that would be a big problem,” said Martínez, who is adamant there will be no major departures from Everton in the next transfer window, a stance that applies to John Stones and Romelu Lukaku.

“But for us to have a player of that quality for the money we paid, if we lose him it will be on a profit financially so we would be able to use the money. And you want the player. You’re talking about a Barcelona player who has been all through his years as the golden boy believing he is going to be at the top level at Barcelona and we got him for a very good price. I’d like to tell Barcelona that he’s rubbish but they come to watch our games.”