Cal Crutchlow is in no doubt that reigning MotoGP World champion Casey Stoner is the 'fastest man on the planet'.

The injured Monster Yamaha Tech 3 star also reckons Aussie Stoner has not received the credit he's deserved in recent seasons and admitted he was 'disappointed' by news of Stoner's retirement from MotoGP at the end of 2012.

"It was more disappointing for everyone else than it was for him," Crutchlow said on Stoner's shock decision.

"People don't really give him credit for how fast he is - he is by far the fastest guy on the planet.

"Maybe over the years he just hasn't put the championship together, whether that's because of machinery or himself sometimes, but he's by far the fastest guy and when he did get the machinery, he went and won last year.

"And when he won the title before, he maybe didn't have the best machinery, but he was the best guy," added the Briton, who was speaking during a live webchat with on Bennetts Bike Insurance Facebook page.

"In all honesty he's leaving the sport for reasons that are correct in some ways and him leaving the sport is a wake-up call for some people.

"But if his passion for the sport isn't there any more then I think he's right to retire and he's definitely done a great job and left a legacy as well.

"I think he'll stop and that will be it. He's done everything in motorcycle racing," Crutchlow added.

"MotoGP is the pinnacle and if you can win in MotoGP then that's the top.

"Hopefully for his sake he can win this year for the third time and leave on a high."