Van der Vaart, whose wife Sylvie works for a German TV station nearby Schalke's home ground, would cost the German club around £10million but he is refusing to discuss his future until after Euro 2012.
"His qualities are unprecedented," Stevens told Sky Sports.
"I would love to work with him again. We have contacts with his agent. Every day I speak to Horst Heldt (Schalke’s general manager) on the phone about our plans.
"There are rumours circulating that Rafael would return to Germany. But I have not heard from his mouth. I have not spoken with him and we’ll have to see after Euro 2012 .
"He has a contract so we will have to pay a ransom. If Rafa really wants it, he is welcome.
"If that opportunity arises, and he looks forward to it, let him come."