Former heavyweight world champion Frank Bruno has given Australian Formula One driver Mark Webber the benefit of his advice on when to call it quits. The Red Bull racer told reporters at the season-ending Brazilian Grand Prix on Saturday that he had \"bumped into\" the British boxer, who fought with Mike Tyson and Lennox Lewis, on a visit to his gym a few months ago.\"He\'s been through quite a few things and he\'s been very honest with me the last few times I\'ve gone up there,\" said Webber, 35.\"He said that \'the biggest fight you will have in your career is when you just try to stop\'. And that\'s how it is for all of us.\"That\'s how competitors are -- there\'s obviously some arrogance involved that we want to keep competing.\"Webber, who renewed his Red Bull contract at the end of August for one more year, was talking in relation to Brazilian Rubens Barrichello\'s determination to keep racing for a 20th season in Formula One, but his words suggested the subject of retirement had also been on his mind earlier in the year.The Australian has not won a race this year, after being a title contender right to the last in 2010, in a campaign dominated by German team mate Sebastian Vettel -- now a double world champion.McLaren\'s Jenson Button, who recently signed a new multi-year deal with his team, agreed the question of when to call it quits was rarely straightforward.\"You\'ve got to make sure that you\'re ready to leave because if you leave too early and you try and come back, for a lot if us I don\'t think it will work,\" said the 31-year-old Briton.\"It\'s a difficult call, when you decide to retire, if it is your choice.\"It is not something you take lightly or choose lightly.\"Germany\'s seven-times world champion Michael Schumacher, who retired in 2006 after a record-breaking spell with Ferrari, returned last season with Mercedes but has yet to step back on the podium.He will be joined on the grid next year by another driver making a comeback, with McLaren\'s 40-year-old Spanish tester Pedro de la Rosa signed for HRT.