The Bulgarian midfielder, who was diagnosed with the condition in March last year and is now in remission, has announced he will not play again. Tributes poured in for the fans' favourite, with former Celtic team-mate Lambert describing his friend as a "fantastic player" and "a nice guy with a heart of gold".
Petrov's priority will now be his health and work for his leukaemia charity, but Lambert revealed he is already mulling over a role for the popular captain. "He'll be missed here but the door will always be open for him," said the Scot.
"I have some things in my head which I'm running over. I've something in my head I'm thinking about at the minute and it's not a sentimental thing at all. It's just some things my staff and myself spoke about, they know what I think."
Petrov will lead Villa out for their traditional lap of appreciation after Saturday's final home game against Chelsea.
Villa fans and their opposition counterparts have shown support for Petrov with 60 seconds of applause in the 19th minute of every game since he fell ill, in tribute to his squad number. Lambert knows Saturday's farewell will be particularly poignant.
"For him to lead out the team will be a great occasion," said the Villa boss. "I think it will be pretty emotional for him when he does it on Saturday."
Lambert added: "Not having him around here during his illness has been a huge blow, it can never be underestimated.
"Him not playing has been massive for this club. Having to try to replace someone like that - a footballer who is a fantastic player - has been hard.
"He has a heart of gold, he's nice guy. I knew him since he was 19 years of age and he first came to Glasgow and I had a good friendship with him. I played with him for nine years and he was always someone you knew you needed to be in the trenches with you."
- Sports & Recreation