Messi, 31, is enjoying another spectacular season, scoring his 50th career hat-trick in a LaLiga win over Sevilla on Saturday to move onto 33 goals in 32 games this campaign.
Ahead of Madrid's Copa del Rey semi-final second leg against Barca on Wednesday, Van der Vaart spoke about the attributes that make Messi unstoppable.
"He's from another world," he told El Larguero.
"I saw him the other day against Sevilla. It's impossible to stop him, I think so because he appears everywhere.
"He runs with the ball but between speed and technique, you cannot defend him."
Van der Vaart hopes his former team advance to the Copa del Rey final, with the tie locked at 1-1 heading into the encounter at the Santiago Bernabeu.
The former Netherlands international recalled a Clasico he featured in a decade ago when Messi and Thierry Henry scored braces in a 6-2 league win for Barca in Madrid.
"When I was in Madrid, Barca were much better than us, much better than all the other teams in the world at that time," Van der Vaart said.
"I remember the match [that finished] 2-6, it looked like a PlayStation game."