Vlaar insisted he is desperate for the deadly duo to stay after their contribution this term.
He said: "I don't know much about the situation with Andi. I know about his contract but I don't know much more. It's between him and the club.
"The way he is playing at the moment is very good, he's in good spirits and he's found a bit of form. He has to decide what he wants. It will be great if he stays with us."