Mauricio Pochettino is ready to veto a new contract for Tottenham star Jan Vertonghen amid a decline that can partly be explained by mystery ankle problems, Football Insider can reveal.

The defender, 32, has been a mainstay of the Argentine’s six-season reign but his struggles have been at the heart of Spurs’ wretched start to the season.

A Tottenham source has told Football Insider that Pochettino and his coaching staff are concerned about the drop in Vertonghen’s performance levels and the manager isn’t convinced he should be handed the contract extension he is seeking.

The 118-times Belgium international is also being increasingly affected by ankle issues, which the coaches feel is affecting his mobility over 90 minutes.

Vertonghen out of contract at the end of the season, by which time he will be 33.

Football Insider revealed last month that the centre-back, 32, is eager to extend his seven-year spell at the club with another deal.

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Vertonghen has re-established himself in the Tottenham team after being omitted for the first three matches of the season, when Davinson Sanchez partnered Toby Alderweireld in central defence.

The long-serving Belgian pair were joined by Sanchez in a three-man defence in Saturday’s 1-1 draw against Watford, but they once again looked ill at ease.

Vertonghen has started the last eight Premier League and Champions League matches, but there are fears that his best days are behind him following a glittering top-level career for club and country.

Tottenham’s decision-makers won’t hand Vertonghen a new contract without seeing a significant improvement in his performances.

In other Tottenham news, Paul Robinson has exclusively spoken to Football Insider about “horrible injury” that is a sickening blow to Spurs.