The value of Valencia forward Juan Mata has risen by around €10 million since Sunday after the expiration of an agreement between the player and his current employers.
Arsenal and Tottenham were in contact with the Spanish side with a view to signing the 23-year-old this summer and the player's father revealed on Monday that the Gunners' bid for his son had been rejected.
Mata signed a new contract last summer after interest from Barcelona failed to develop into something more concrete, and the player's buy-out clause was set at a prohibitive total of €60 million.
Nevertheless, Mata and his father - who is also his agent - established a genteman's agreement with Valencia, by which the player could leave for a fee of around €25 million before August 1 of this summer.
That deadline was aimed to protect the club and allow coach Unai Emery time to bring in a replacement should the player leave Mestalla.
The date has now come and gone, however, and Arsenal's last-minute attempt to sign the player at a cut-price fee ended in failure on Monday.
The Gunners are thought to have offered less than the €25 million fee quoted by Valencia and will now need to substantially up their offer in order to sign the World Cup winner.
Tottenham, meanwhile, were prepared to meet the Spaniards' asking price, but the player himself is unkeen on a move to White Hart Lane, seeing Spurs as an inferior option to his current club.
Mata's father claimed on Monday that Arsenal were set to return with an improved bid for his son, and also revealed that Inter had been in touch with a view to signing the 23-year-old.
Liverpool also showed interest earlier in the summer, after Mata had led Spain's Under-21 side to European Championship glory in Denmark, but the Reds have dropped out of the race after signing winger Stewart Downing from Aston Villa.
Mata could yet leave Mestalla this summer, although the club have no intention of selling and, now in a strong bargaining position, are likely to ask for up to €35m for their in-demand player.
Nevertheless, Valencia now believe they will hold on to their forward and coach Emery has been told that recent recruit Sergio Canales, signed from Real Madrid this week, was brought in to complement Mata - not to replace him.