Valencia - Three-time MotoGP world champion Jorge Lorenzo, who suffered a fractured spine this year, said Thursday he would retire following this weekend's season-ending Valencia Grand Prix.
The 32-year-old Spaniard, who rides for Honda and claimed the world title in 2010, 2012 and 2015, told a press conference he was pulling out following Sunday's race.
The rider, who was also twice crowned 250cc champion, was retained for next season by Honda but has suffered from poor form and serious injuries this season.
"This will be my last race in MotoGP and after this I am retiring from professional racing," Lorenzo said.
"I've always thought there are four significant days in the life of a rider -- the first one is when it's your first race, the second one is your first win, then your first world championship -- not everyone can win the world championship, but some of us made it.
"And then the day you retire. As you all imagine here, I'm here to announce that this day has arrived for me."
Lorenzo said that a series of spills earlier this season with Honda led him to consider retiring for the first time in his career.
"Injuries came to play an important role in my results and my performance so I was not able to be in a normal physical condition to be fast," he said.
Lorenzo fractured his spine in two places during opening practice for the Dutch Grand Prix on June 28, bouncing into four somersaults and hitting the gravel behind his bike.
He described how he was picking himself up off the gravel when he made a snap decision to quit the sport.
"'OK Jorge, is this really worth it after what I have achieved'," he said. "'I am done with it, I don't want to race any more'."
Later he had a rethink and returned to the circuit.
"The truth is from that moment the hill became so big and high for me I couldn't find the motivation to continue to climb," he said.
His Honda teammate Marc Marquez, who wrapped up his sixth top-class world title last month, said Lorenzo's decision was a surprise.
"It was a surprise even for his teammate because in the team we didn't know," said the Spaniard.
"He's a true champion and when he felt he couldn't be at the top, he decided to stop, and this shows his strength of character on and off the track."
Seven-time MotoGP world champion Valentino Rossi hailed his former Yamaha partner, saying: "Jorge is one of the greatest MotoGP riders of the modern era.
"We are losing a very important part of our sport, a great champion."
Lorenzo joined Honda on a two-year deal for the start of this season, but is languishing in 19th spot in the riders' standings, with a best finish of 11th in May's French Grand Prix.