Australia's Michael Doohan, who won the 500-cc motorcycle championship five times between '94 and '98, has announced his retirement from the sport. The 34-year-old, who ranks as one of motorcycling's greatest ever riders, has been plagued by injury problems since his high speed crash at the Spanish Grand Prix. Since crashing at Jerez, Doohan has undergone intensive medical attention but to no avail.
