Valentino Rossi says that soon to be former Petronas Yamaha team-mate Franco Morbidelli is 'fighting against time' following knee surgery, but will attempt a MotoGP return next weekend at Misano.

Reigning title runner-up Morbidelli was forced to undergo surgery in late June after suffering repeated issues with the meniscus and anterior cruciate ligament in his left knee.

While Morbidelli's home Misano round has long been targeted for a comeback, it should also mark his debut for the Factory Yamaha team, as a replacement for Maverick Vinales.

"Franco together with Carlo [Casabianca, VR46] is fighting against time," Rossi said at Aragon on Thursday. "Because the surgery was serious, because the injury to the knee of Franco was quite bad.

"So they made a deep surgery, everything is good, but the rehabilitation is very strong and I saw Frankie suffer a lot. A lot, a lot of effort every day and now in the last period it's improved and he will try for Misano and I hope that he can be good."

As well as using Vinales' factory-spec M1, Morbidelli is expected to finish the season with the Spaniard's former team members, including crew chief Silvano Galbusera, currently working with test rider and temporary stand-in Cal Crutchlow.

However, the Englishman, who is set to focus on testing and development of the 2022 M1 after Aragon, revealed on Thursday that Galbusera will remain at the race team for the rest of this year.

But Morbidelli may yet be reunited with his Petronas crew chief Ramon Forcada – set to finish the season with Andrea Dovizioso - at the Factory team for 2022.

Another Italian getting access to the very latest machinery next season will be Rossi's younger brother Luca Marini.

Like Morbidelli (at Petronas), Marini has an ageing 2019-spec bike (Ducati), but with VR46 taking over the Avintia entry next season, Rossi confirmed the #10 is set to get a GP22 machine.

"Next year Luca will be in a good situation because looks like we can have a Ducati 2022 and I think that it's better than his current bike, so I think that he can be more competitive," said Rossi.

"My advice [to him] is to give the maximum, train always at the best also at home, because I think that next year he can have a good chance to show his speed and potential."

The only VR46 Academy rider on the latest factory bike at the start of this season was Official Ducati rider Francesco Bagnaia.

Still seeking a first MotoGP victory, Bagnaia has been runner-up three times this year but also suffered some major setbacks with tyre performance, most notably at Silverstone, where he plummeted from second on the grid to 14th.

Bagnaia said on Thursday that Michelin had "recognised that my rear tyre was not competitive".

Rossi also struggled badly for tyre grip at Silverstone, but the Italian made clear his issue was caused by colder temperatures forcing him to run the medium rear.

"Pecco was very strong all weekend at Silverstone, except the race. So it's a different situation [to mine], more strange," Rossi said.

"For me personally unfortunately the problem is a bit worse. I mean for me these tyres are very soft [construction], and I always suffer with this. Especially in the last years because the latest rear tyre is also softer [construction].

"In Silverstone I had some chance to make a good race if we can use the hard [compound] because with the hard in practice I was a lot faster. But unfortunately it was too cold so we had to choose the medium and unfortunately after 5-6 laps I was already in trouble.

"I don’t ask nothing [from Michelin]. We have to try to find the solution to improve, it depends from track to track because for example Silverstone is a very demanding track for the rear tyre.

"Looks like that in the future also already from next year maybe the tyres will change a little bit, but unfortunately for me it's too late! So we have to try the maximum to the end," added Rossi, who will retire at the end of this season.

The nine-time world champion missed last year's Aragon rounds, where the factory Yamaha riders struggled badly with cold October conditions.

"Last year I didn’t race because of Covid unfortunately," Rossi said. "But the conditions are very different, because last year the problem was that it was too cold. Now it looks like it'll be very hot. So we need to understand the way to work on the bike and the tyre to use."

Aragon has never been a particularly successful track for Rossi or Yamaha, with present title leader Fabio Quartararo labelling it as 'probably his worst circuit'.

"This is a very important race for Quartararo because on paper Aragon is not a Yamaha track," Rossi said.

"In the past we always suffer, especially the rear tyre degradation so it will not be easy but if we can be strong and competitive also here in Aragon, I think it's very important for his championship.

"But every year is different and we need to understand from tomorrow the work of the tyre on this track."

Quartararo starts the 13th round with a 65-point title lead over Suzuki's Joan Mir. Rossi is currently just 21st in the world championship.