Roberto Martínez has warned David Moyes that Everton will not sell Marouane Fellaini for a reduced fee now the midfielder's £23.5m buyout clause has expired.

Moyes is interested in adding the Belgium international to Manchester United's midfield but made no official move to sign Fellaini before the release clause elapsed on 31 July. It is believed Moyes is reluctant to pay over £18m for a player he bought for £15m from Standard Liège in 2008.

Fellaini, Everton's record signing, is under contract at Goodison Park for another three years and has not attracted any offers so far this summer. Martínez has not ruled out the prospect of selling the 25-year-old, admitting that: "If there is an offer on the table then we will have to look into it." But he told his predecessor as Everton manager that any plan to sign Fellaini for under £23.5m would be doomed to failure.

"When you are in a strong position financially you will never sell a player for less than the buyout clause," Martínez said. "Marouane had that clause in his contract, it was very clear for everyone, and on the 31st of July it expired. From that point on, the club has got complete control, in every single transfer, and that's the way it should be. It's the right approach for all parties. Yes, you are sweating on July 30th, 31st, but after that it is just a matter that we don't have to sell players because we are not in a situation where we need an amount of money to balance the books. We are not in that situation at all. We don't have bags of money but we don't have to sell any players."

Moyes sought to protect Everton with the date of Fellaini's buyout clause having seen preparations for the 2009-10 season undermined by Joleon Lescott's late move to Manchester City. And, as Martínez pointed out, he could have submitted an offer below £23.5m before 31 July.

The Everton manager explained: "The buyout clause gives you control as a buyer. It doesn't mean you have to pay that money. We've had no approaches for Marouane Fellaini. Just because you have a clause it doesn't mean clubs are stopped from putting a bid in for less money, but it's never been the case that we had an offer. What the clause does mean is that if someone meets the valuation you haven't got a say as a club, and as a manager that worries you because you don't have a decision to make.

"If there is an offer on the table then we will have to look into it. I have always said that as a club you need to be able to cope with any situation. If you lose a player you need to be able to replace him. There is never a manager or a player who is bigger than the football club. The recruitment department at Everton and every department at the club is ready to cope with any situation that is thrown at us."

Martínez could return to his former club, Wigan Athletic, for James McCarthy in the event of Fellaini leaving Goodison but insists he has no desire to part company with the influential Belgian. "I think clubs maybe know that he has been very, very happy at Everton," said the manager on the lack of bids. "Also, this window is different than others because the World Cup is around the corner and players don't want to unsettle their routine. At Everton we want to keep our best players and keep on improving window after window. If you lose players it becomes harder."

Everton rejected United's £12m offer for Leighton Baines earlier in the summer and, despite his 11-year reign at Goodison and close relationship with the chairman, Bill Kenwright, Martínez does not believe Moyes's past will deter him from bidding for former players. "That would be a very nice way to work in football but managers don't think that way," said Martínez, who signed Arouna Koné for £5m from Wigan.

"When you are a manager you don't think about your past or what might be seen as socially acceptable. United made it clear it was their final offer [for Baines]. If someone tells you it is their final offer it should be their final offer."