Michael Schumacher has insisted that Ferrari bosses did not pressure him into announcing his retirement.
Schumacher says his decision to retire was his alone
There were rumours that Schumacher was forced into a decision so Ferrari could name their drivers for next season.
And Formula One boss Bernie Ecclestone told Sport-Bild magazine on Wednesday he felt "Michael had to make a decision when he really didn't want to".
"Ferrari were incredibly gracious and left it all up to me to say when," Schumacher said.
"I know there has been much speculation but the timing of the announcement was right for me."
Schumacher said he began to have doubts during the weekend of the Turkish Grand Prix last month whether the Italian race was the right place to make the announcement.
"I wondered whether to wait until the end of the year," Schumacher said.
There is simply no proof that Alonso had blocked Massa
He added that he spoke to Ferrari team boss Jean Todt during testing the week after Turkey and "decided to tell everyone after the Monza race because I wanted to be able to focus on it beforehand.
"I'm not getting any younger and I had to ask myself if I would be able to gear up the energy, strength and motivation that you must have in order to be able to compete at the top.
"Of course I'm still fit, still competitive, but would I be for a few more years?
"Just being a mediocre driver has never been my ambition. That's not my style."
Schumacher is now just two points behind world champion Fernando Alonso in the race for the drivers' title.
The German benefited from the controversial decision to penalise Alonso five places on the starting grid after blocking Ferrari's Felipe Massa in qualifying - a punishment criticised by Ecclestone, who described it as a "farce".
"There is simply no proof that Alonso had blocked Massa," he said.