By Tom Fordyce BBC Sport Online

For most of us, the chance to quit your job at the age of 33, already a multi-millionaire, is the stuff of wild fantasy.

Retirement? A delightful notion, replete with images of long lie-ins, relaxing days lazing in the garden and several holidays a year.

But for top sportsmen, choosing when to bow out of their chosen sport is one of the hardest decisions they will ever have to make.

Venus's father has advised her to retire

Do you keep on keeping on until your body can take no more, happy to sacrifice success for the pleasure of taking part?

Or do you duck out at the top, wanting to be remembered as a winner rather than an also-ran?

Former F1 world champion Damon Hill thinks his old sparring partner Michael Schumacher might be on the brink of calling it quits.

On the face of it, it's a strange idea. Schumacher dominates his sport, earns millions a season and says he is still obsessed with winning.

But Hill, who retired aged 39 when the wins had dried up, thinks the 33-year-old Schumi may be nearing the end.

"Michael's entire body language suggests he's not getting the same kind of enjoyment from winning as he used to," said Hill.

"While Ferrari are the current dominant force, there is no guarantee Michael will be so competitive next season.

"He may well feel it's best to bow out while at the very top."

Jordan found it impossible to stay on the sidelines

It is hard to envisage Schumacher, a proud and intensely competitive man, carrying on if he was relegated from the front few rows of the grid.

The danger, of course, is that the tame reality of life outside motor racing will be impossible to deal with.

Bjorn Borg called it a day at the tender age of 26, realising that John McEnroe had his number and that his time as number one was up. It didn't help.

No tennis meant no direction, and that meant business problems, personal crises and an unsuccessful comeback, when he even tried to use a wooden racquet in an age of titanium frames.

Michael Jordan enjoyed more business success than Borg but still found life post-sport empty and unsatisfying.

Running the Washington Wizards was fine in theory. What it meant in reality was watching players inferior to himself failing to even play with the same commitment as he had done.

The solution? Four hours in the gym each day and another comeback at the age of 38.

Venus Williams, still only 21, has already been urged by her father Richard to leave tennis behind.

"I told Venus two or three years ago that she should retire. I really think she should," he said in April this year.

"Venus is a rare human being when it comes to education, business and business knowledge," he said.

"She has a rare quality that every now and then you see in life. I've tried to get Venus to understand that."

Luis Figo, world footballer of the year and Champions League winner with Real Madrid last May, is another to consider retiring while in his pomp.

Figo's enthusiasm is rumoured to have waned

"I'm going to call it quits much sooner than people believe," said the 29-year-old recently.

"I don't want to abuse my fame and I'm not afraid of retiring."

On Wednesday, former world middleweight boxing champion Felix Trinidad, the same age as Figo, called time on his career in the ring.

Trinidad's father, Trinidad Rodriguez, who also serves as his son's trainer and manager, said: "Tito has finished his career healthy, with a brilliant record.

"And, thanks to God, with an economic future that guarantees peace for him and his family for the rest of his life."

Schumacher has had that security for years. Whether that comforting thought has dulled his desire for a scrap remains to be seen.