The 22-year-old handed the Midlands club a major boost when he withdrew a transfer request and agreed a new deal until 2017.
The striker netted 19 goals as Villa escaped the drop last term and Petrov believes Benteke could make all the difference in the coming campaign.
He said: "It's a big boost. The way he performed last season, the way he played, if Villa had lost him, they would probably be in bigger trouble.
"Keeping him is just great. All the fans, the players, the manager, everybody is happy that Christian is staying at the club.
"He has shown unbelievable potential. He is still a young boy and he still has a lot to learn.
"But, if he plays the way he played last season, Villa will finish very, very high this season."
Petrov sees no reason why the Belgian should receive stick from Villa fans as a result of his initial plans to quit the club.
He said: "I don't think so, I don't think they should give him stick.
"They should actually be pleased that they have a player like that in their team.
"In the last couple of years, Aston Villa sold a lot of players.
"A lot of players went to Liverpool, Manchester United, Manchester City.
"When you have a season like Christian had, of course you have ambitions, of course you are going to have clubs with ambitions who are after you.
"I think the fans will be even happier now that Christian has decided to stay with the club."
On Villa's prospects for the campaign ahead, Petrov said: "I think they'll have a very good season.
"The manager has a very exciting young squad.
"They have got a long way to improve still but they are hungry, they want to achieve, they want to be counted and I think they will do well."
Petrov announced his retirement from football in May following his battle against acute leukaemia.
Today, back at Celtic Park where a legends charity match will take place in September to celebrate his career, he spoke of his heartbreak at being forced to hang up his boots at the age of 33.
He said: "It was very hard. It's what I wanted to do all my life. I wanted to become a professional footballer - play football, enjoy football.
"It was really difficult when I got the news, it was heart-breaking. I burst into tears, I couldn't believe it.
"Obviously I knew a lot about my disease, I knew the treatment and everything, but I didn't know it was going to be that hard and that long.
"The advice from my professor and the doctors was that I couldn't continue to play football because of a lot of reasons - the steroids, the tablets, the bones getting weaker.
"It's a thing that you can't risk and, at the moment, the most important thing is my health."
He added: "I've been offered a job to work with the reserve team at Villa.
"I've been doing it for two weeks and I've been in the dug-out for a couple of games and I really enjoy it.
"It's something new for me, something exciting and I'm really happy to work with these young boys.
"The next step is setting up my foundation, which is a big thing.
"I went through a lot last year and I will try to help and make a difference."
He is also confident his former club Celtic will be able to cope without Gary Hooper if the striker quits the Scottish champions.
It is understood the Hoops have accepted a bid for the 25-year-old from QPR.
Norwich and Hull had offers turned down earlier this year but the player could now be on his way to Loftus Road after both clubs reached agreement on a fee.
Hooper has netted 82 goals in three years in the east end of Glasgow and came off the bench as Celtic eased into the third qualifying round of the Champions League at the expense of Cliftonville last night.
But Petrov believes boss Neil Lennon will be able to attract a suitable replacement for Hooper should he seal his departure.
He said: "Will he stay or go? I'd love to see him stay.
"You could see the difference when he came on last night, the way he plays.
"You just know big clubs will come after him.
"But, as long as Celtic get enough money, and they are happy with that and the player is happy, I don't think it will be a problem.
"Celtic always attract good players and, if he goes, there will be somebody else who will come in."
Celtic reached the last 16 of the Champions League last year and Petrov knows the knockout stages will be the aim again this time around but he says simply booking a place in the group stages of the competition must be seen as success.
He said: "I think that will be Neil Lennon's target, to reach that level again.
"But even if they don't, qualifying for the Champions League will be enough I think.
"It's very important, as a club and financially, to make the group stages but it's going to be really tough.
"Every club realises how important the Champions League is, especially financially.
"Every club, when they play in the play-offs, spend a lot of money and they try to build a strong team.
"Celtic have come through this round and the next couple of rounds will be even harder but I think they're ready for it."