Alli, who has been linked with Real Madrid and Paris Saint-Germain, joined Tottenham in a £5m deal from MK Dons in 2015 and scored 10 times during his first campaign in the Premier League.
The England international has already scored 13 times during the 2016-17 season, meanwhile, and at the weekend, it was claimed Manchester City boss Pep Guardiola was desperate to bring the attacker to the Etihad Stadium in a world-record deal.
Dier, however, has called on his teammate Alli to continue his development at White Hart Lane, where he is "very well looked after".
"He's still a very young boy, I think people need to remember that. He's at the perfect place for that because he's got a support system around him and a manager and a group of players that will take care of him," Dier told Sky Sports News.
"You have to worry about young players sometimes in certain places if they can cope with it and will they be looked after as a 20-year-old boy and not just an asset. I think he's very well looked after here and hopefully he will be for a long time."
Alli started his professional career with MK Dons, representing the club 88 times before joining Tottenham, who are said to have snatched the youngster out of the clutches of Liverpool.