'Schumacher shouldn't have come out of retirement'

Michael Schumacher should have stayed in retirement rather than risked his reputation in a disappointing Formula One comeback with Mercedes, Bernie Ecclestone said on Friday.

"I would rather he had stopped as a seven-time world champion than stopping now," the commercial supremo told the official formula1.com website.

"People new to the sport -- people who have joined the F1 fan fraternity just recently -- will remember Michael now, not as he was. They don't see the hero that he was but the human that can fail," added the 82-year-old.

The 43-year-old German had first retired in 2006, when he was with Ferrari and had won five titles in a row with them to add to the two championships he won with Benetton in the 1990s.

Ecclestone, whose own future at the helm of the sport has been increasingly questioned as legal problems mount up and he gets older, drew a parallel with his own situation although he made clear he had no plans to retire.

"I think the important thing is...to know when you can't do what you used to do anymore and then hand it over to somebody else. I hope that's what I can do: when I feel I can't deliver, I will certainly say goodbye," he said.

Ecclestone said Formula One would continue to explore new frontiers, with Russia's Sochi the next new race to be added to the calendar in 2014 now that a grand prix in New Jersey had been postponed for 2013.

"I suppose the next big thing will be Russia. Then we have to get this New York thing picking up again. There's lots of unfinished business - no time to waste one thought on retirement," he said.

The Briton hailed the debut of a new race in Austin, Texas, this year as phenomenal and "perfectly prepared" and sent a warning to European circuits that they needed to sharpen up their act.