Michael Schumacher will call time on his painfully uncompetitive F1 comeback and return to retirement two years earlier than planned at the end of the 2010 campaign - that is the opinion of two of the sport's most well-recognised figures, Sir Jackie Stewart and Bernie Ecclestone.

Schumacher signed a three-year contract with Mercedes Grand Prix last winter to make a much-hyped and celebrated comeback to active competition three years on from originally hanging up his helmet. Since then, however, the driver who broke all records in F1 by claiming no fewer than seven world championship trophies, 91 grand prix victories, 154 rostrum finishes and 1,369 points between 1991 and 2006 has sadly been little but a shadow of his former self, with mediocre performance after mediocre performance seeing him tally a mere 36 points with no finish higher than fourth place. In stark comparison, young team-mate and compatriot Nico Rosberg has notched up 90 points and a trio of podiums.

The younger German has also out-qualified his elder countryman eight times out of ten, and at Silverstone last weekend the 25-year-old was some eight tenths of a second quicker than the man who was once unbeatable. Race day witnessed more of the same - third place for Rosberg, a distant ninth for 'Schumi', with a difference in lap time of some 1.2 seconds.

The man himself might continue to insist that he is enjoying his second bite at the F1 cherry and has every intention of mounting a renewed title challenge in 2011 [see separate story - click here], but the disappointingly listless form displayed by the Kerpen native this season has prompted Stewart - who walked away at the top of his game after clinching his third career crown at the highest level in 1973 aged just 34, seven years younger than Schumacher is now - to muse that the end may well be nigh, and definitively this time.

"He cannot even keep up with his team-mate," the Scot told the Cologne-based newspaper Express when asked whether he believes the most successful driver in the sport's history can yet take the fight to the likes of Lewis Hamilton and Sebastian Vettel, adding that Schumacher should swallow his pride and call it quits come season's end before his illustrious reputation suffers any more damage. "He (Rosberg) is usually faster and has not won a grand prix.

"I would have preferred to have seen Michael not come back. 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.

"The first question should be 'will he do another year?' I believe he will stop after this season. What does his heart say? I will believe it only when I see him on the starting grid in March."

Those sentiments are echoed by influential F1 commercial rights-holder Ecclestone, who has invariably defended Schumacher but now similarly concedes that his return may have been an ill-conceived and ill-fated one.

"He is obviously fit, motivated and talented but the car hasn't been up to him," the British billionaire acknowledged. "If Schumacher doesn't perform, I doubt whether he will want to stay."