Francis Coquelin has played like a £40m player since Christmas, according to his Arsenal boss Arsene Wenger.
The French midfielder's Emirates days appeared numbered when he was sent to Charlton on loan last year, but injuries elsewhere earned him a recall and he has since made himself an indispensible member of a Gunners side beaten just four times in 2015.
A new contract has been agreed, but Sky Sports' ex-Arsenal players Paul Merson and Thierry Henry are among those who believe Wenger should sign competition for the holding midfielder this summer.
The Arsenal manager is not ruling out that prospect but has backed Coquelin to hold his own even if reinforcements arrive.
"The world has changed," Wenger said. "The appreciation today of the quality of a player is just down with the money you spend.
"If we had bought Coquelin at Christmas for £40m, everyone would say 'what a signing'. I am sorry he didn't cost any money, he is still a good player.
"What is a player worth today? Nobody knows really. I just wanted to say that if we had bought (Coquelin), nobody would complain that he was a good player.
"Nobody would dispute that his performances have been convincing and that he is ready for a fight even if somebody comes in. He has shown he has the capacity to play for us and play a big part in the success of the team. I extended his contract, that means I believe in him."
Wenger's priority is to keep "the core of the squad" together this summer, and any new additions will be made against the backdrop of Arsenal's 'self-sustaining' financial policy.
Reflecting on UEFA's imminent relaxation of its Financial Fair Play rules, he said: "I have no problem to lose the battle. I just did fight for what looks to me to be logical: that any business, to have a continuity, should live with the
resources that it creates. It doesn't look like anything absolutely unbelievable.
"We have to see what happens now, what will be respected in the Financial Fair Play and what will go out of the window, I don't know."