AUSTIN (Texas) - Retired sprint king Usain Bolt has vowed to pursue his dream of playing professional football but admits he will not embarrass himself if his goal is out of reach.

The Jamaican track and field superstar, who retired from athletics after August's World Championships, has long spoken of trying his hand at football and has been invited to train with German Bundesliga side Borussia Dortmund.

Bolt, the 100m and 200m world record holder and eight-time Olympic gold medallist, insists he is serious about his football dream despite scepticism that at, 31, his age will count against him.

"It's a personal goal, I don't care what people really think about it," he told reporters on the sidelines of the United States Formula One Grand Prix in Austin on Sunday.

"I am not going to lie to myself, if I feel I can't do it, I am going to say 'Forget this'. I am not going to embarrass myself.

"It's a dream, it's another chapter of my life that I really want to do. If you have a dream or something you really want to do, you want to try to see where it could go."

Bolt has had a long-standing invitation to train with Dortmund, an arrangement facilitated by his long-time sponsors Puma.

However, the Jamaican has not taken advantage of the Bundesliga side's offer yet because of a niggling hamstring problem.

He said: "They said the invitation is always open, so it is all about me getting over my injury and into shape. Then I can explore it and do the trials and see what level I am at.

Bolt, however, admits that he is not optimistic about being granted a similar opportunity with the club he supports, English Premier League giants Manchester United.

"It would be difficult to convince (Jose) Mourinho, but we never know, it's something I said to (ex-manager) Alex Ferguson the other day when I was there," he joked.

A role with the International Association of Athletics Federations (IAAF) could also be an option.

"I am waiting to see if my football career is going anywhere, but I definitely want to work with IAAF, in ways to promote the sport, to keep the sport at the level which I left," Bolt added.

"I want to use my name to promote our sport, like an ambassador role."

AGENCE FRANCE-PRESSE, REUTERS