Isco has been in and out of the Madrid team this season, not having started a La Liga game since late October. The 26-year-old has been repeatedly linked with a move away from the Spanish capital amid reports he is unhappy with his role.
The former Malaga star could be given a chance to claim his place in Santiago Solari's team when his side face Ajax in the Champions League knockout round, and Van der Vaart hopes to see him in action when the Dutchman's former teams go head-to-head.
"Isco is crazy for me, the best player in the world," Van der Vaart told Marca. "But he always has problems with coaches. Zinedine Zidane never trusted him 100 per cent. When Ajax play Madrid, I'll see if he starts. If he is not, I'm going home.
"I really want to see that match between two great teams. Ajax are impressive, have many talents and win all their games playing fantastic football that I like to see. They go on the attack, they score a lot of goals, they have a spectacular team. It will be a very complicated match for Real Madrid, for sure.
"It is difficult to give a prediction. In Netherlands, people think that Ajax is going to win for sure, but I want to remind you that Madrid in the Champions League is Real Madrid. It is a difficult game for Ajax. They will have chances to get through, but they should be at the top to be in the quarter-finals."
And Van der Vaart feels they are no longer favourites to win the Champions League, as his former team-mate's move makes Juve the side to beat this season.
"Right now everyone recognises how important he was for Real Madrid, someone who was scoring almost 60 goals per season," he added.
"The team that has Cristiano in its ranks will always be a favourite. He makes his team-mates better. You give him the ball and you know he can score, he guarantees success."
Van der Vaart also touched on in-demand Ajax stars Frenkie de Jong and Matthijs de Ligt, who are still being linked to some of Europe's best teams.
"I want them to stay in Amsterdam, but it is normal that they are receiving offers from the best because they play really well. They are impressive talents, they are at the top of the world and surely have a very big career.
"Although they are also very young, they must go step by step. De Jong reminds me of Guti, he has a lot of quality and he handles the ball as you would want from the centre of the field."