Weimann is impressed with the rebuilding job of Lambert, who has made major changes to the playing squad in a short space of time.
He told Villa's website: "He's brilliant to work with. He's doing an unbelievable job when you look at it.
"He's completely changed the team. From when he arrived, he's transformed the look of the squad.
"That's not easy - doing that, being competitive and winning football matches but he has managed that superbly.
"We're now sitting 12th in the table in his second season in charge. I know it's very tight but we feel positive about our position and the remaining weeks to come. We have progressed as a group, definitely.
"I know we have had some great wins and some frustrating defeats but when you look at it overall, you can see how far we have come as a group.
"We are determined to stay up there in the table and push forward now.
"I can't see how the gaffer could have done any better. He's done a top job."