The midfielder struggled to make an impact at White Hart Lane during his first campaign with the club, but he has emerged into a key player for Spurs in recent months.
Vertonghen, who also plays with the 25-year-old for Belgium, believes that fans are now seeing the 'real Chadli'.
"It's great that he's growing. He's a very good player and it's a shame he couldn't show what he is capable of last year but now we're seeing the real Nacer," he told the club's official website.
Spurs continue their Premier League campaign on Saturday when they travel to champions Manchester City.