Before joining Tottenham Hotspur in 2010, van der Vaart netted 12 goals in 73 appearances during a two-season spell with Real.
Los Blancos have endured a difficult La Liga campaign this season but are determined to retain the Champions League – evident from their impressive last-16 victory over Paris Saint-Germain.
Meanwhile, Manchester City look set to win the Premier League this season and are among favourites to be crowned champions of Europe.
Van der Vaart believes Real are the only team that can stop the Sky Blues from such an achievement.
“Madrid is a great club with fantastic players and facilities. [When] they played against PSG, the Parisians had money, but they still couldn’t beat Real Madrid.
“I think Madrid still has got the quality to win the Champions League again. But I’m a little bit surprised that they’re not doing well enough in the La Liga.”
“I think the only one (who can stop City) is Real Madrid.”
There has been a huge difference between City and Los Blancos in their domestic leagues this season. Guardiola’s men have been by far the better side.
However, Real’s European success clearly still counts for something. They have netted 22 goals to City’s 19 in the Champions League and have created 133 chances across their eight European matches, while City have created 80.
Real face Juventus in the quarter-finals, while City have an all-English clash with Liverpool.