Sir Jackie Stewart has tipped Michael Schumacher to re-retire at the end of the year, amid continuing sub-par performances for Mercedes Grand Prix.
Asked by German's Cologne Express newspaper if he thinks the seven-time World Champion and winner of a record 91 grands prix is still capable at age 41 of keeping up with the likes of Sebastian Vettel and Lewis Hamilton, Stewart replied, "He cannot even keep up with his teammate. He (Nico Rosberg) is usually faster, and has not won a grand prix.
Stewart, who retired in 1973 at the age of 34 as a three-time World Champion and subsequently resisted offers to return to racing, added that in his view, Schumacher was ill-advised to attempt a comeback after years away from the sport.
"I would have preferred to have seen Michael not come back," Stewart told the newspaper. "Why did he do it? He had achieved everything and could only lose.
"In my opinion he retired too early, he should have stayed another two years with Ferrari and I have no idea why he didn't. Now he's in a difficult situation and has to live with the criticism."
When asked if he thought Schumacher could improve in 2011, Stewart expressed doubt that Schumacher will stick with his comeback.
"The first question should be, 'Will he do another year?' Stewart said. "I believe he will stop after this season."