Will Power will miss the rest of the IndyCar season after sustaining two broken vertebrae in his lower back in a practice crash at Sears Point last weekend.
The Australian, who won for Penske at Edmonton in July, came over a blind crest during the Saturday practice session and found Nelson Philippe's Conquest Racing car sitting broadside across the track after the Frenchman had spun.
He had no time to react and speared into the side of it just after it had been clipped by Ernesto Viso.
Power suffered a heavy concussion as well as the fractures to his second and fourth lumbar vertebrae, and Penske team president Tim Cindric confirmed that he would not be fit to race again this season.
"It's unfortuante because we wanted to end the season on a high with him," said Cindric. "We are working on a deal with him for next year."
Power is still being treated at Santa Rosa Memorial Hospital in California and has been fitted for a customised back brace.
He is expected to be transfered to a hospital in Indianapolis in the next two days where he will undergo further examination by the IRL's orthopedic specialist Dr Terry Trammell.
Power began the season alongside Ryan Briscoe at Penske, but had to make way for Helio Castroneves when the Brazilian was cleared to race following his tax evasion trial. The team then added a third car for him from the race at Toronto in July.
Philippe suffered a concussion, an open fracture of his left foot and a hairline fracture of his right fibula, but has been released from hospital in California.