Will Power and Nelson Philippe were transported to hospital after an accident during practice for the IndyCar Series race at Sonoma's Infineon Raceway.

Philippe, who was returning to the championship with Conquest Racing this weekend, had spun over the blind crest on the exit of Turn 4 and come to rest with his car parked on the racing line.

HVM's EJ Viso was first on the scene and clipped the front end of Philippe's car with his left-rear wheel, breaking his suspension and smashing the Conquest Dallara's front wing. Power arrived moments later and was unable to avoid plowing into the side of Philippe's machine. 

While Viso was uninjured, both Power and Philippe had to be removed from their cars under medical supervision, and Penske driver Power was transferred to Santa Rosa Memorial Hospital by helicopter for back pain to be assessed. It has subsequently been determined that the Australian suffered fractures of his L2 and L4 vertebrae.

Philippe was transported to the hospital by ambulance with an open fracture to his left foot. The Frenchman underwent surgery Saturday afternoon, and will be hospitalized overnight.

Penske Racing boss Tim Cindric said that there were no plans to enter an alternative driver in the 12 team's backup car. "It's either Power or nobody," he said.

Asked if Power will still be racing in Homestead, the season finale in October, as originally planned, Cindric said: "At this stage, nothing is definite until we know more."