"We've seen it in other clubs," he told London's Evening Standard newspaper on Tuesday. "Even if he has a contract, you can't force somebody to play for you."
Real Madrid coach Carlo Ancelotti said last week that the La Liga club were in talks with Spurs to buy Bale, with speculation mounting that the 24-year-old, voted English Footballer of the Year last season, wants to move for a world-record fee.
Bale is still under contract at the north London club, where chairman Daniel Levy is renowned as a tough negotiator as Madrid discovered when buying Croatian midfielder Luka Modric from Spurs last year.
Spurs have strengthened their squad for the coming season with the addition of Brazil midfielder Paulinho from Corinthians, in a deal worth 17 million pounds, and Belgium winger Nacer Chadli from Dutch side Twente Enschede for a fee that media reports said was in the region of seven million pounds.
On Monday, they confirmed the club-record transfer of Valencia striker Roberto Soldado for 30 million euros (£25.84 million).
The club missed out on Champions League qualification by one point last season and Mills said the new arrivals had brought the club hope that they could reach Europe's premier club competition for the second time.
The loss of Bale, however, even for a fee reported to be in excess of 85 million pounds, would be a blow for their ambitions given the Welshman's outstanding performance last season.
(Reporting by Josh Reich; Editing by Clare Fallon)
