The on-loan striker would have to take a drastic pay-cut on his Manchester City wages to make the move.
"I think the problem is the wages," Van der Vaart said.
"Yes, I have tried to persuade him to stay.
"Last season I had a good understanding with Peter Crouch, but with him it's even better. He's tall and strong. He's not selfish and his attitude is one of the best."