Dier, 21, has been in superb form this season, with manager Mauricio Pochettino switching the England Under-21 ace from right back and centre back to a holding midfield role.
His role is primarily to protect the back four, but Dier has also chipped in with goals in a superb start to the new Premier League season, becoming a key player under Pochettino so far this term.
With just one defeat this season - which came on the opening day of the season against Manchester United - Tottenham are thriving under Pochettino, and whilst they only drew 2-2 with Swansea City on Sunday, they did come back from behind twice in order to get their draw.
It once again showed Spurs' resilience, but their fitness levels were once again a factor, with Tottenham coming on strong late in the game to almost snatch a victory.
It's been a recurring theme under Pochettino, both last season and this term, with Tottenham kicking on in the dying stages, often to great effect.
Now, utility man Dier has told the Daily Mail that Premier League rivals simply can't handle Spurs' fitness levels, citing that it's a huge part of Pochettino's philosophy at White Hart Lane.
"We are one of the fittest teams in the League. If you look at the stats on how much ground our players cover in a match, I think we are always up there," said Dier. "I don't think many teams can handle our fitness. Manchester City couldn't and nor could Swansea. We keep going for 90 minutes and teams drop off."
"Fitness is a big thing for our manager and his staff. They work us hard. The pre-season was all about running and building up your fitness. Let's just say, you get your trainers out!" he added.
With a young, vibrant squad and a manager whose focus is on fitness levels, Spurs should be able to give most teams a real challenge this season - and whilst other teams are tiring late on, Spurs will be looking to claim points late in the day, which will be a huge factor for Pochettino this season and going forward.