The 22-year-old Austrian found the net 12 times last season, but he has only been on the scoresheet four times during the current campaign.
Despite Weimann's waning form in front of goal this term, Lambert is confident that the youngster will show signs of improvement soon.
"I think people are missing the point with him because he's only really been playing regularly for about a year," the Scot told the Birmingham Mail.
"I know he was in and out the team the season before last when he'd just come through the academy. It's only probably since we came in that he's had a sustainable run at it. Last year he was excellent, this year I think more times than not he's played well for us.
"I think people think he's been round for years and he's played a couple of hundred games and things like that. If you look at his experience he's not played that many games."
Weimann signed his first professional contract with Villa in 2010 following a spell in the club's youth academy.