Alli has quickly risen from a young prospect to one of the key players in the Premier League today, having only made his Tottenham debut at the start of the 2015/16 season.
Since then, he has made over 100 appearances, helped Spurs to a second-place finish last season, as well as scooped up the PFA Young Player of the Year award.
Alli also truly announced himself on the world stage this season when his double helped the north London side to a famous 3-1 victory over Real Madrid in the Champions League group stage.
The former MK Dons midfielder's exploits have seen him attract the interest of Madrid, while Barcelona are also monitoring Alli as a potential Philippe Coutinho-alternative.
And former Tottenham midfielder Jermaine Jenas believes when clubs of those calibre come calling, Alli simply cannot miss the opportunity.
"Should he stay at Tottenham? I don't know," Jenas was quoted as saying by the Mirror. "What he's achieving at Spurs is brilliant and he'll play the games there, that's the guarantee.
"But you can't ignore it if Real come or Barca come. And they are the two clubs, essentially, because I don't see him moving within English football. Maybe Manchester City, if they start dominating European football, might start being attractive to him.
"But for that legacy element, if Real or Barcelona come calling, then you have to go and have that experience – otherwise you'll regret it for life."
Jenas adds that the 21-year-old also shares the same mentality as the best players in the world today, in that, he aims to reach for the stars rather than remain grounded.
"You get told to keep your feet on the ground, but, as a player, you don't want to think that – you need to be reaching for the stars," Jenas explained.
"Watching Dele, you can see that he has that attitude – the kind of attitude that the best players in the world have. He's on the right path and, hopefully, he'll be performing at the top level in the World Cup."