Italian veteran Valentino Rossi says racing at his 400th MotoGP is a "great achievement".
The 40-year-old is a nine-time world champion and is competing in his 24th season at World Championship level.
Rossi will remain in the sport until at least 2020 after signing a two-year contract extension with Yamaha in 2018.
"I never ever had a clear idea how long I want to race," said Rossi, who will compete at the Australian Grand Prix in Melbourne on Sunday.
"It's something that you don't expect. It's been a long, long time."
Rossi crashed out of the Japanese Grand Prix last weekend and is currently seventh in the standings with three races remaining.
"When you get good results out there everything is easier because you enjoy it more," he said.
"But if you are in a difficult moment then there is motivation also to try and come back."
Remarkable Rossi - facts you need to know
- Rossi has started 42.5% of all Grands Prix.
- He has won 115 races across all classes and scored points in 353 of them.
- Rossi is the only rider in history to win World Championships in 125cc, 250cc, 500cc and MotoGP.
- He suffered a double leg-break in 2017 but returned just 21 days later to compete at the Aragon GP, despite needing a stick to walk. He finished fifth.
- He has won more races at at Phillip Island, Melbourne, than any other racer, with eight.