Nico Rosberg doesn't believe Lewis Hamilton is performing at a higher level this year compared to last season when the German beat his Mercedes team mate to the title.
Rosberg clinched the championship in 2016 in Abu Dhabi and is back in the Yas Marina paddock this year, working with German broadcaster RTL.
Pundits have suggested that Hamilton has upped his game this season, and Rosberg is well placed to offer his view on the matter.
"I know what level he was driving at last year and I'm probably the best judge of that," said Rosberg.
"I would say no. I don't think he could have improved.
"During the season he had his strong and weaker moments, and like I did last season, Sebastian (Vettel) tried to use those weaknesses.
"But the difference this year was that, unlike in 2016, Lewis did practically all of Mercedes' wins.
"Last year we drove at such a high level throughout the season that Valtteri (Bottas) had a very difficult job to try to continue in the same way," Rosberg added.
Assessing his former team's achievements in 2017, the 32-year-old retired driver has been very impressed by Mercedes' ability to transition from one set of rules to the other, and retain its success.
"To survive a rule change like that with such dominance is very, very rare in Formula 1," he said.
"It was the next step to legendary status for Mercedes."
But Rosberg also took his hat off to Ferrari, praising the Italian outfit for its progress and success.
"You have to see their performance increase as a kind of miracle," he said.
"There was confusion in 2016, a big change of personnel -- they were in no man's land," he said.
He also viewed Ferrari's collapse in reliability towards the end of this year as "normal", because the Italian team was simply "on the limit" of what is possible in F1.