Felipe Massa continues to promote his own agenda, claiming that Robert Kubica would be physically challenged to perform consistently behind the wheel of a new-spec car.
Williams is narrowing down its options for its 2018 driver line-up with Massa, Kubica, Paul di Resta and Pascal Wehrlein all in contention for a seat at the Grove-based outfit next season.
Kubica ramped-up his F1 comeback program over the summer, with runs in a 2017-spec Renault in Hungary and two outings in a 2014-spec Williams at Silverstone and again at the Hungaroring.
Massa is skeptical however of the Pole's ability to race and perform consistently in F1 given the limited ability of his right arm.
"I have no idea how he's driving, first of all," he said in an exclusive interview with Motorsport.com's GP Gazette.
"To be honest, I cannot do what he's doing, driving with only one hand.
"It's impossible for me to believe that he will not suffer with some of the races with this car that we're driving that is a lot more difficult physically.
"I really respect what he's doing, and what he's doing is just amazing. But it's impossible to believe that he will not have some issues."
As he grind his axe, Massa also took a shot at di Resta, claiming the Scot's results in DTM with Mercedes these past seasons were nothing to write home about.
"I don't believe he's the right driver for the team, to develop the car and show the results and everything," Massa said.
"Plus I mean I don't think he's doing a great job in what he's racing as well. Anyway, I'm not here to complain or say about anything, that's only my opinion."
Massa insisted however that he would show no frustration should Williams opt not to include the Brazilian in its line-up next season.
"Yeah, sure, but I'm good on that. I have zero frustration. As I've said before, I did a lot more than I expected.
"So if it needs to finish, it's the time. If it doesn't need to finish, it's because maybe something is still reserved.
"As I said, I'm quite relaxed, thinking about my job, thinking about my car. The time for being frustrated is passed already in my career."