As part of the FOTA peace deal, 69-year-old Mosley pledged not to contest another election, but he was subsequently angered by the reaction of the breakaway group and said he was reconsidering his options.
"He said his options are open but he didn't say what they were going to be, did he?" Ecclestone, the F1 chief executive, said in a new interview for the Times, less than a week after controversially commenting about Adolf Hitler.
He explained that Mosley's threat to do a u-turn on his promised resignation was because he was "a bit upset" with Luca di Montezemolo's public reaction to his impending exit.
Ecclestone said at the Nurburgring: "I have no doubt in my mind (he will retire). As long as I've known Max, he's always done what he said he would do."
The 78-year-old was speaking amid rumors the FOTA teams and the owners of F1's commercial rights, CVC, have sidelined him in their latest negotiations over a new Concorde Agreement.
Late on Friday, Britain's Guardian newspaper said in a headline: "Formula one teams bypass discredited Ecclestone to seek 2010 resolution".
07/10/09 (GMM) Ari Vatanen has admitted the possibility he may have to fight incumbent Max Mosley in the FIA presidential election later this year.
The Finnish former world rally champion and European Parliamentarian, at the Nurburgring this weekend, on Friday announced his intention to succeed 69-year-old Mosley at the head of F1's governing body.
Mosley has indicated he wants to retire, and therefore Vatanen's announcement was interpreted by some as a move towards a smooth handover of power.
But Vatanen, 57, said: "Maybe Max is still standing, it's not been excluded at all. There's not (been) a decision."
Interestingly, Vatanen's comments come after he spoke on the telephone with Mosley to inform him of his candidacy, according to the Associated Press.
Leading figures of the FOTA alliance, who quietly believe Mosley's resignation would avert the breakaway threat, were not commenting about Vatanen on Friday but it is suggested they support him over the incumbent.
Vatanen indicated his presidential campaign will be based on the need for conciliation.
"There has been far too much time on the battle ground instead of being on the common ground," he said. "There are far too many quarrels for secondary reasons."