SONOMA, Calif. — Will Power of Team Penske was still being evaluated at a hospital Sunday, a day after breaking two vertebrae in his lower back and sustaining a concussion during a crash in practice for the Indy Grand Prix of Sonoma.

Power collided with Nelson Philippe of Conquest Racing during practice Saturday. Philippe also sustained a concussion along with an open fracture to his left foot that required surgery.

The 28-year-old Power, a former road course specialist who finished fifth in this year's Indianapolis 500, crashed into Philippe coming out of a blind corner at Infineon Raceway.

Team Penske said it's too early to say whether Power will miss the rest of the year..

"We just don't know yet," spokesman Merrill Cain said.