Daly wrote on his Twitter page that he had "no choice" to pull out despite finishing 12 holes of the third round at the weather-delayed tournament.
He said the injury stemmed from his piriformis muscle.
"[B]asically my hip dropped an inch on swing & escalated to my back nerve & dropped me to my knees," Daly wrote.
Playing on a sponsor's exemption, Daly made the 36-hole cut Saturday on the number. He was one-over par and 15 shots off the lead when he withdrew.
