The Toffees boss says the club will listen to offers for the Belgium international but only if they match or exceed the 23.5 million pound buyout clause that expired on July 31.
The Belgium international has been heavily linked with a summer move to Manchester United to link up with former boss David Moyes, but no formal approach has been made as of yet.
The clause in the ex-Standard Liege midfielder’s contract ceased to exist on July 31, and while Martinez said the club would be willing to listen to bids, he insisted the player will not be allowed to leave for anything less than the clause's worth.
"If there is an offer on the table then we will have to look into it," Martinez told reporters. “When you are in a strong position financially you will never sell a player for less than the buyout clause.
"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.”
Fellaini, who is Everton’s record signing having arrived from Standard Liege for 15 million pounds in 2008, and he remains under contract at Goodison Park for another three years.