Weimann has 17 months left of his remaining deal - worth around £15,000 a week - and there has been speculation that negotiations have stalled over the terms of a four-year contract offer.
But Lambert wants to keep hold of the Austria Under-21 international, who has netted 10 times this season, and insists Weimann is happy at the midlands club. He said: "Have contract talks stalled? No, we are still talking. Contrary to reports, I spoke to Andi the other day about it and he has never once indicated what the report said."
Lambert added: "I've spoken to him and everything is fine. Talks are ongoing but that's normal when you are trying to negotiate.
"Andi loves it here. I've spoken to him. I think there are more important things at this moment in time than worrying about contracts.
"What will happen with his contract will happen. He's still under contract so at the minute it's fine. I don't think he'll walk away. I don't."
Lambert added: "I think everyone knows agents can inflate people's salaries to whatever it is going to be. I think Andi's been very good and I've no problem with him at all. He's concentrating on the next 11 games. I've spoken to him a few times."
Villa striker Darren Bent is doubtful for Monday's home clash against Barclays Premier League champions Manchester City with a foot injury.
Lambert will also check on the fitness of captain Ron Vlaar, who missed last weekend's defeat at Arsenal with a calf problem.
He said: "Darren is still struggling with a knock on his foot which is a little bit of a concern.