Casey Stoner faces a crucial test of his fitness ahead of his return to MotoGP racing at the Japanese Grand Prix six weeks after surgery to his right ankle.

The two-time world champion will assess his recovery from ligament surgery in opening practice sessions on Friday at the Motegi circuit.

Stoner has missed the last three races because of the injury he sustained during qualifying for the Indianapolis GP in August.

He is now out of contention to retain his 2011 title which will be decided between his teammate Dani Pedrosa and Yamaha rival Jorge Lorenzo.

He admits it has not been easy recuperating while watching the races on television with Pedrosa and Lorenzo battling for the title.

"The last six weeks have been pretty tough for me, I've had to sit around and rest my ankle, get some physio and try to occupy my time but I've been watching the races at home," Stoner said.

The demands of the stop-go Motegi circuit with areas of hard braking and acceleration will be a tough test for Stoner's return to racing.

The Japanese GP is the first step in his campaign to be fully fit for his home race, the Australian GP at Phillip Island, in two weeks.

"Motegi is pretty tough on the body and physically quite demanding," Stoner said.

"The first session on Friday will be crucial to see how my ankle feels in the boot and the degree of movement I have and pressure I can apply."

Before the surgery to repair seriously torn ligaments Stoner feared that he may not have a full range of movement and strength in his ankle.

His last race appearance was eight weeks ago with a brave fourth place, riding with pain killing injections and an oversize boot for his swollen ankle, in Indianapolis.

Stoner is currently third with 186 points having won four races.

Lorenzo leads the championship with a 33 point margin over Pedrosa, 290 points to 257, with four races remaining.

Stoner is due to retire from MotoGP at the final race of this season in Valencia in November.