The Welshman is in the midst of the most prolific season of his career so far, having netted 19 goals in 31 appearances to lead Spurs' challenge for Champions League qualification.
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He wrote in his column for the Daily Mail: "A year playing like this in the Champions League and he will be in the £70 million bracket.
"Big clubs will offer big money. But maybe it's time for him to give Tottenham a bit back. The club are growing, with talented players and a good manager. With one or two acquisitions Spurs can challenge for the title next year."
Bale's recent run of form has seen him compared to Real Madrid star Cristiano Ronaldo, but Waddle believes it is too soon to mention the two players in the same breath.
"Sometimes we're accused of going overboard in Britain, judging players on three of four games," he continued.
"Bale's been incredible for a couple of months. We'd seen glimpses of what he could do. Now he's doing it every week.
"He's come of age this season, adding consistency, but he has to deliver this form for four or five years before we can start talking about him at the same level as Lionel Messi and Cristiano Ronaldo."