Petrov is in remission after undergoing chemotherapy following his diagnosis in March 2012.
The Bulgarian is now able to visit Villa Park and the club's Bodymoor Heath training base on a more regular basis and he will watch from the stands on Monday night when Villa face Manchester United at Old Trafford as they fight for their Premier League survival.
Lambert played with Petrov at Celtic and has praised him for his positive attitude in adversity and for the effect that has on everyone at the club.
"First and foremost it's great that he's in remission and as he said, he's going to try to live a normal life," said Lambert.
"I don't think anyone could envisage what he's been through, unless they have themselves. It puts everything in perspective.
"The 19th minute of applause (Petrov's squad number is 19) at the games is fantastic, from home and away fans.
"I've known him since he was 19 when I first played with him and never in a million years did I think anything like that would happen to him, he's such a fit lad.
"Thankfully, he's doing great. He did a little bit of work with the fitness guys the other day. It's great that he's on that road.
"When he comes into the building I'm pretty sure everyone will have a thought in their head, thinking 'my God, he's done that' about what he's been through. You wouldn't be human otherwise.
"It puts things into perspective and the lads love to see him, which is nice."
Petrov himself was impressed with his team-mates' attitude ahead of their crucial run-in.
"There's five games to go, I've been to see the boys this week and they're really up for it," he said.
"They're playing, creating chances and it's great to see, especially from a young team. The young lads have picked up their form and are sticking to it and not giving up.
"Sometimes when you go on a bad run you just give up, but all these young boys have got stuck in."