Although Keselowski himself said x-rays were negative after being examined at hospital on Wednesday, doctors said there was an avulsion fracture to his left ankle.
However, the injury will not hamper him from racing next Sunday.
Sam Hornish Jr, who raced for Penske until last year in Cup, was set to be on stand-by at Pocono on Friday but, following the latest diagnosis, he will concentrate on replacing Keselowski in the Nationwide Series race at Iowa, taking his place from Friday's practice sessions.
Keselowski was lucky to scape relatively unharmed from a massive shunt suffered in testing on Wednesday at Road Atlanta, where he was running in preparation for the upcoming Cup event at Watkins Glen. The incident took place at Turn 1 and was caused by a suspected brake failure, according to the Penske driver.
He was set to race at Iowa in the Nationwide Series on Saturday besides his Cup duties, but following the accident it was decided Keselowski would focus on the Pocono race.
"After meeting with Brad Keselowski today it became clear that, despite an avulsion fracture of the left ankle, he would be able to compete this weekend at Pocono Raceway without any limitations," said Dr. Jerry Petty according to a release from Penske Racing.
"Mr. Keselowski saw an orthopedic surgeon this afternoon who indicated that he would be able to put weight on the foot as necessary and should not be inhibited in any way."
Had Keselowski been unable to race the distance at Pocono on Sunday, he would've been able to benefit from NASCAR rules by handing his car to a relief driver following the start. According to the rules, the driver starting the race is credited with the finish, regardless of him not being behind the wheel at the flag.
