Bayern go into Saturday's clash having scored nine goals and only conceded one in their first two fixtures of the league season.

They put six past Stuttgart in their last match, with Thomas Mueller grabbing a double.

And Heynckes feels that result demonstrates his team's desire as they seek to end a two-year drought without winning major honours.

"It shows the team is hungry and has rediscovered its appetite," the 67-year-old told the official club website.

"We have to prepare very thoroughly, because it'll be a hard job. They (Mainz) are very difficult opponents."

Bayern look set to give new 40 million-euro midfielder Javi Martinez his debut but Heynckes knows they cannot underestimate the visitors, who inflicted a shock 3-2 defeat on his team last season.

"We have to be just as aggressive as we were against Stuttgart, accept the rules of engagement laid down by our opponents, and exploit our footballing class in attack," he said.

Bayern are without the services of Mario Gomez, David Alaba and Diego Contento through injury.

While there is still concern over Toni Kroos' fitness with a groin injury,  Arjen Robben is now fit again after missing international duty with the Netherlands last week.