Petrov is retiring after a 14-month fight against acute leukaemia and plans to set up a foundation to help sufferers of the disease.
But the offer to stay on at Villa Park in a backroom role is there, according to manager Lambert, who played alongside the Bulgarian at Celtic.
"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 spoken about, they know what I think.
"Not having him around here during his illness has been 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."