Stoner retired from MotoGP in 2012, as a two-time champion, aged just 27 claiming he no longer enjoyed the sport.

Marquez, for different reasons, was at his lowest ebb earlier this year but his Ducati debut at the postseason Valencia test restored his smile.

Stoner told TNT Sports at Phillip Island: “If you’re not enjoying it, why are you risking it all?

“If Marc enjoys his racing, he’s not going to want to risk it all for nothing.

“It’s important for him to get that enjoyment back. Find a reason to get up in the morning, train your butt off, put yourself through these injuries, drag yourself back.

“People see it from the outside. But it’s very difficult when everything is against you, your body doesn’t want to do things, but you force it. It takes a toll.”

Eight-time world champion Marquez has suffered three years of career-threatening injuries and an underperforming Honda.

This year at the Sachsenring, traditionally one of his favourite tracks, he looked more solemn than ever after five crashes before the grand prix itself forced him to withdraw.

But, now aged 30, the early signs of his decision to quit Honda for Gresini Ducati are that a new bike could breathe life into his career.

Stoner, 11 years ago, was unable to find a reason to continue.

He commented on his decision to quit early: “If you’re going to risk everything, to lay everything on the line, you’ve got to do it for a reason.

“Some people find it’s money. Or for whatever reason they do it, for a result.

“For me, I just loved riding bikes. Racing was a part of it. I got to race, it was fantastic.

“I loved riding bikes the most, I loved eking everything that I could out of a bike. I was very self-critical.

“When these bikes became too much electronics, too much wheelie-control, the enjoyment disappeared.

“The series became political.”