Canadian Robert Wickens is being treated for injuries to his lower extremities, right arm and spine following an accident early in the A-B-C Supply 500.
IndyCar said the native of Guelph sustained a pulmonary contusion and will undergo an M-R-I and probable surgery.
The 29-year-old was attempting to pass Ryan Hunter-Reay when the two cars slightly touched, sending the former's car spinning through the air into the fence.
Alexander Rossi was the winner at Pocono.
Rossi raced to his third victory of the season for Andretti Autosport and second straight.
He also won on the streets of Long Beach in April and the Mid-Ohio road course three weeks ago.