Mata, who was part of Spain's World Cup-winning squad last year and led the Under-21 side to glory in the European Championship earlier this summer, has repeatedly claimed to be content at Valencia.
Nevertheless, transfer speculation has continued and the player has been linked with the likes of Arsenal, Liverpool, Manchester City and Tottenham this summer.
His coach, Unai Emery, admitted that Valencia may sell if a big team comes in with an attractive offer, telling Cadena Copa: "Valencia has to be prepared for a footballer having to leave, either because is he is not wanted or because some big club wants to sign him.
"We want him to stay and Mata has also expressed his wish to remain at Valencia, but we know that if a big-money offer comes in from any club and it's good for both the player and the club, it could lead to his exit."
But Mata says he is focused on his current club and, in remarks reported by Marca, said: "I have never said I want to leave.
"From here to August 31, if there are any offers then the first to know about it will be the club. I never said I wasn't happy here.
"There's no point speaking about suppositions. I like to talk about realities. I am very relaxed because if there is anything, the club will assess it.
Mata claims he is used to dealing with transfer talk, in any case, having been tipped to move to Barcelona during last summer's World Cup and then heavily linked with several sides during the recent Euros.
"For me, isolating myself is no problem," he said.
"I already went through it at the World Cup and at the European Under-21 Championship.
"I know the boss said something yesterday (about the possibility of me leaving), but I am not aware of any offer having arrived."