A.J. Foyt was released released from a Houston, Texas hospital Saturday after tests determined the four-time Indianapolis 500 winner was suffering from a bruised kidney.

The announcement was made by a team spokesman at Michigan International Speedway, where Foyt, 53, had been scheduled to drive in Sunday's Marlboro 500 before his hospitalization on Thursday after suffering severe stomach pains.Foyt has been racing in the NASCAR stock car and IMSA sports car series' this year, as well as attempting to run the entire 15-race Indy-car series for the first time since 1978. He drove in a 500-mile stock car race last Sunday at Talladega, Ala., finishing 12th and on the lead lap on a steamy afternoon.

"The doctors said I must have twisted myself getting in and out of my stock car at Talladega and it broke a blood vessel in the bottom of my kidney," Foyt said in a telephone call from his home in Houston.