The cash-strapped La Liga side - currently third in the table - rejected offers in the region of 40 million euros for the Spanish international during the summer.
However, Los Che are now believed to be ready to part company with the 28-year-old - who tops the La Liga goal-scoring charts this season with 11 - as they can no longer afford to ignore such a large amount of money.
Villa had stated his intention to remain in Spain during the close-season - with both Barca and Real thought to have come close to agreeing a deal - although he has since admitted that a transfer to the Premier League would appeal.
But Mestalla manager Emery insisted that, while the club are on the lookout for a potential successor to Villa - who has scored 98 league goals in 143 games for Valencia - he will not be sold until a suitable replacement is found first.
"The exit of Villa will be dependent on us identifying a suitable replacement," he told Sky Sports.
"At the moment the club is working on that, but any decision will not rest with me.
"My mission is to prepare the squad for the present and not think too much about the future. Valencia will always be a big club and we do not depend on just one or two players."
Villa joined Valencia in 2005 after former Chelsea boss Claudio Ranieri signed him from Real Zaragoza.
He has made 54 appearances for Spain, scoring 35 goals and was part of the European Championship-winning side in 2008 where he also won the Golden Boot.
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