The Bulgaria international has been undergoing chemotherapy since being diagnosed as suffering from acute leukaemia three months ago. But it did not stop Petrov from celebrating his 33rd birthday by attending Villa's first day of pre-season under new manager Paul Lambert at Bodymoor Heath.
Petrov, who played alongside Lambert at Celtic, said: "It has been hard. I can't say it has been easy. It has been hard but I didn't expect anything else. Life is hard and we live in it."
He added: "I have just gone through it. I have had good days, I have had bad days, ups and downs. That is the way it goes.
"But I have a lot of hope and I haven't stopped believing since the start and I will never stop believing. My family believe as well. It is a great help when you read messages and you've got letters from people who have beaten this already and they have already lived 20 or 30 years.
"You just say to yourself, 'I am going to be there as well'. I am just not going to stop fighting. I have always been a fighter and I will just keep fighting."
On the football front, Petrov has faith in former Norwich boss Lambert to revive Villa's fortunes after they avoided relegation from the Barclays Premier League by two points last season.
He said: "I played with him for seven years at Celtic and I am really happy that he has got the job at Villa.
"I am really confident that he is going to do very well for this club because I know him very well. He is really looking forward to working at this club.
"I know the boys will have a great season. I said that the season before wasn't great and we wanted to show we didn't have a great season last season."
Source: PA
Source: PA