Petrov believes there is plenty more to come now that his fitness problems seem to be fading into the past.
"I can relax a little because when you come to a club with a big name, you want to impress the fans, your team and your manager," he told the Bolton News. "You want to show you are a good player.
"I know the first few games have not been easy, and that I haven't shown my best form. But I am trying to train more and am hopeful that I can continue like that.
"Everyone must know what they need to do in their position in the team.
"Fitness is a big part and I stay behind in many training sessions, knowing that I need to work more and more."