The 21-year-old has progressed into a key figure at Spurs since joining the club in 2015 and was recently crowned PFA Young Player of the Year for the second season in succession.
Van der Vaart is impressed with the youngster's performances this campaign and believes he is destined to become one of the best around in the game.
"It is just a pleasure to see Alli play," Van der Vaart told the official Tottenham website.
"He is still so young and already so eager, I like that a lot. He is fast, fluid and has a great skill set.
"He is special and if he keeps enjoying himself and the game, he may become a true great.
"I hope everyone will give him his time to develop to his full potential. It is not easy in the Premier League for young players and perhaps even less so for the British talents because all eyes are on them.
"I hope he is having a great time on the pitch and at the club. I wish him well."