It was the final lap at Sunday's race in the Reliant Stadium area when Franchitti's car was involved in a wreck that sent debris in the stands, injuring more than a dozen spectators.
Franchitti suffered a concussion, a fracture to the spine and had surgery on his right ankle.
"I'm overwhelmed by the outpouring of support and I'm thankful to have such a great family and such wonderful friends and fans," said Franchitti. "Thanks to everyone at the hospital and the track who took such good care of me during my stay in Houston."
Franchitti will now go to Indianapolis, where he'll be reevaluated and await a second surgery to his ankle.
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