(CNN) -- Valentino Rossi's hopes of retaining his MotoGP title were shattered on Saturday when the nine-time world champion motorcyclist suffered a horrific crash in a practice session for his home race in Italy.
The 31-year-old could be out for months after fracturing a shin bone in his leg when he was thrown from his Yamaha in the second session ahead of qualifying at Mugello.
He had an operation on Saturday afternoon, the official MotoGP Web site reported, after being flown to Careggi Hospital in Florence and then moved to the orthopedic trauma center.
"It's an injury more serious than we thought, because it's an exposed fracture with the bone protruding from the skin," Doctor Claudio Macchiagodena of the sport's traveling medics Clinica Mobile told motogp.com.
"We have reduced the fracture, which fortunately has not affected any blood vessels or nerves. It is serious."
Doctor Roberto Buzzi, who performed the operation, said Rossi would be ruled out for at least two months.
The rider, known as "The Doctor" among other nicknames, could miss eight races, starting with Sunday's Italian Grand Prix -- which he has won nine times.
"The surgery had good results," Buzzi told motogp.com. "The alignment was good and the bone is now stable.
"The wound remains open, as is usual in these cases, and it will be stitched in the next few days with another short surgery. We are confident that Valentino will be able to leave the hospital in a week to 10 days, able to put weight on the leg with the aid of crutches.
"It is difficult to say how long the post surgery rehabilitation will take. But I think that we can reasonably think of six weeks of partial weight-bearing with crutches, after which Valentino needs to be re-evaluated."
Rossi has not missed a race since his debut in the 125cc class in Malaysia in 1996, but his record run of 230 successive GP starts will now end.
He is second overall in the world championship standings this season, nine points behind Jorge Lorenzo of Spain, who will start Sunday's race second on the grid behind compatriot Dani Pedrosa.
Australia's former world champion Casey Stoner qualified third ahead of Ducati teammate Nicky Hayden, whose veteran fellow American Colin Edwards was fifth on a Monster Yamaha Tech 3.
Pedrosa is fourth overall, 30 points behind Lorenzo, as he seeks his first win of 2010.
Lorenzo is seeking his third successive victory in what is the fourth race of the season.
"I want to say how sad I am for Valentino. I know how bad it is to be injured, especially at your home race, and it looks very painful for him," the 23 year-old told motogp.com.
"I hope he recovers quickly because the championship will not be the same without him."