Vlaar has been impressed with Villa striker Weimann's contribution in his first full season of top flight football - 11 goals to date - and hope he signs a new contract.
Weimann has 15 months remaining of his current contract and is in talks about a new deal.
Vlaar 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."