Valentino Rossi, one of motorcycling's greatest and most charismatic champions, has announced his retirement from MotoGP at the end of the 2021 season after a quarter of a century in grand prix racing.

The 42-year-old Italian, who races with the number 46, is a nine times world champion with seven of his titles won in the top category.

"I decided to stop at the end of the season," he told a specially arranged news conference ahead of this weekend's Styrian Grand Prix at Austria's Red Bull Ring.

"Unfortunately this will be the last half season as a MotoGP rider. It's difficult, it's a very sad moment because it's difficult to say and to know that next year I will not race with the motorcycle.

"I do this thing for more or less 30 years. Next year my life will change. But anyway, it was great, I enjoy very much this long, long journey and it was really, really fun."

Rossi is riding for the Malaysia-based Petronas Yamaha team this season but his form has faded, the veteran languishing 19th in the championship with a best finish of only 10th from nine races.

The sport and his army of fans will miss him nonetheless, the Italian still very much a crowd favourite with global recognition.

The only rider to have started 400 or more races, Rossi has 89 wins from the top category and 26 others from the junior 125cc and 250cc categories.