Petronas Yamaha expects to be without the injured Franco Morbidelli for the next four rounds of the MotoGP World Championship.

The reigning title runner-up was forced to withdraw from Assen and undergo surgery to repair the meniscus and anterior cruciate ligament in his left knee, damaged in recent training accidents.

An 'eight-week rehabilitation programme' was initially predicted, a timeline that suggested Morbidelli might be ready to return after the upcoming Austrian rounds on August 8 and 15th.

But SRT team principal Razlan Razali believes Silverstone (August 29) and Aragon (September 12) are also unlikely and that Morbidelli won't be back until his home Misano round on September 17-19.

"Franco is recovering well from his knee surgery. We want to ensure that he is at 100% before he comes back, so I think that we won’t expect him to be racing again until Misano – although I wish it will be sooner," Razali said.

"This is a track that he loves, he knows well and it should be a good one to see his return at. We all continue to wish him well in his recovery and to come back only when he feels completely fit."

Yamaha World Superbike rider Garrett Gerloff took Morbidelli's place on the A-Spec M1 at Assen, but the American cannot ride at Austria 1 due to a clash with the Brno WorldSBK round.

Triple MotoGP race winner and new Yamaha test rider Cal Crutchlow is among the list of obvious candidates for the Red Bull Ring events, which could also serve as preparation for a popular entry (either with Petronas or as a Yamaha wild-card on a Factory-spec bike) at his following home Silverstone round.

Crutchlow might not be the only big name returning to the grid in Austria, with KTM test rider Dani Pedrosa mulling over the option of a wild-card.

Morbidelli, who took Petronas Yamaha's only podium of the season so far with third place at Jerez, claimed his first ever MotoGP win at Misano last season.