Two-time world motorcycling champion Casey Stoner is set to call it quits on his V8 Supercar experiment at the end of the year.

Stoner, who has been driving for Red Bull Racing in this season's second-tier V8 series, is understood to have decided not to continue in 2014.

The 27-year-old has struggled for most of the year to handle the transition from two wheels to four.

While he has been speedy in qualifying and managed a top-five finish in July at Queensland Raceway in the Dunlop Series, much of his racing has been at the back of the field.

He crashed out on the first corner at Winton last month, before finishing mid-pack in his other two races.

Stoner was not considered for a co-driver's spot for this year's Bathurst 1000.

A Red Bull Racing source was tight-lipped on Stoner's future.

But he says the team expects Stoner to see out the remainder of his one-year deal, which involves second-tier series races at Bathurst in October and the Sydney 500 in December.