Casey Stoner has some frank advice for MotoGP championship leader Marc Marquez: be more respectful.

The straight-talking Australian on Saturday said while the 20-year-old rookie had shown impressive form this season, he warned his successor at Repsol Honda to watch his mouth when he is not racing.

"I think Marc's done a fantastic job this year, without a doubt," said two-time world champion Stoner, who retired at the end of last season.

"We've seen him come up through the ranks, get quicker and quicker, grow a lot of maturity in a lot of ways.

"But I still think he could do things maybe off track just a little bit nicer and be slightly more respectful with some of the things that have happened on track.

"Ok, they're racing incidents. But I think in his words he can be slightly more respectful of what's happened and what it's caused."

Marquez has been criticised for his hard-riding style that has led to a number of crashes this season - including a last-lap clash with Yamaha factory rider Jorge Lorenzo in May's Spanish GP and an incident with teammate Dani Pedrosa at Aragon last month.

The Spaniard was handed a one-point penalty for the contact he made with Pedrosa, who crashed out of the race after his sensor cable broke in the collision.

But that won't stop Marquez from becoming the youngest ever MotoGP world champion on Sunday - provided results fall his way.

He currently holds a commanding 43-point lead over Lorenzo and will only need to outscore him by eight points at Phillip Island to secure the 2013 crown.

It's an achievement that Stoner admires.

"I think he's had a stellar year, unbelievable, and I look forward to seeing what he can do in the future," the 28-year-old said.

"We said this last year and I said it at the beginning of this year that we weren't really too sure what he was going to be able to do. We weren't too sure of the level of Moto2, Moto3.

"But now we see that the level was very high and especially at Marc's level."