Despite being on the cusp of a third World title, Jackie Stewart says one "can't use the word great" to describe Lewis Hamilton just yet.
Hamilton could wrap up his third Drivers' Championship title this weekend at the United States Grand Prix.
Should he outscore Sebastian Vettel by nine points and Nico Rosberg by two he will equal Stewart's tally of three World titles.
But, the Scot says, that doesn't make him a great.
He told Reuters: "He's a top-flight racing driver. You can't use the word great while they are still racing in my opinion. It takes years passing to get that status.
"I don't think almost anybody had it until they were well past. In the case of (double World Champion) Jim Clark, he was great but sadly after he died (in 1968). But he was the leading driver of his time."
The 76-year-old, who in the past questioned Hamilton's decision to swap McLaren for Mercedes, was also full of praise for the Brackley squad and their dominant display.
"It's a remarkable team," Stewart said. "He made a choice of that team and it's delivered for him.
"It's had such domination it could only be compared with the 20s or 30s when the Mercedes Benz and Auto Unions were racing or the 50s when Mercedes Benz came back to totally dominate with Fangio and Stirling (Moss).
"And then I suppose obviously Michael winning all those championships back to back with Ferrari, which was so dominant because of the superiority of their cars.
"It was difficult to judge the greatness of the drivers but we knew Michael was that good."