MotoGP rider Valentino Rossi believes his protege Franco Morbidelli will be a "problem" for him in 2019 on a factory-supported satellite Yamaha.
Now set for his sophomore MotoGP season with the newly-formed Petronas SRT Yamaha team, Morbidelli will ride an 'A-class' M1 similar in spec to factory pair Rossi and Maverick Vinales.
Morbidelli, who rode a Marc VDS Honda in his first year in MotoGP, made an immediate impact in post-season testing and ended up sixth fastest on the final day at Jerez.
"He was impressive on his Yamaha debut, because he was immediately very strong," said Rossi of Morbidelli.
"So next year he will be a problem.
"Franco likes the Yamaha a lot, because it's a very generous bike that gives you good feedback.
"It's a bike that is the friend of the rider, but we lack some grip and he also has the same thing."
Morbidelli will not be the only Rossi protege on the MotoGP grid in 2019, with his successor as Moto2 champion Francesco Bagnaia making the step up to the top class this year with Pramac Ducati.
After taking intermediate class honours this year, Bagnaia - who also shone in Jerez testing - holds the distinction of being the first rider to win a world title for Rossi's Sky Racing VR46 squad.
Rossi was asked to compare the two Italian rising stars and said that while Bagnaia is more naturally talented, Morbidelli is "tougher" and "works more".
"Both are very good riders, as they already have demonstrated," said Rossi.
"Bagnaia is more talented in terms of natural skills, but at the same time Morbidelli is tougher, more difficult to beat.
"Morbidelli works more and is more aggressive.
"I don't know which of them will be faster, but next year they will have similar bikes in terms of performance, so it will be interesting to see them."