WWE.com has learned that Rey Mysterio suffered a concussion at the hands of The Miz this past Sunday at SummerSlam. ( RESULTS)

According to one backstage source, WWE personnel “suspected [a concussion] because he hit his head.” The following day, precautionary impact testing was conducted and “showed that [Mysterio] is below baseline, which means he sustained some sort of concussion,” the source explained.

WWE.com has confirmed that the San Diego native is not medically cleared to compete at this time. Mysterio did not appear on last Monday’s Raw, and has been removed from all events at least through this coming weekend. ( MYSTERIO'S SUPERSTAR PROFILE)

During The Awesome One’s successful Intercontinental Title defense at STAPLES Center in Los Angeles last Sunday, the champion executed a brutal sit-down powerbomb. The maneuver snapped Mysterio’s head against the canvas, which likely caused the trauma and no doubt paved the way for The Miz’s victory. The self-proclaimed “Most Must-See Champion in WWE History” has had his awesomeness questioned in recent months, but The Miz reasserted himself with this dominance over the 619 specialist.

According to WWE physician Michael Sampson, Mysterio “had the first [test] on Monday, which showed us that he was below baseline. The physical exam was normal, but neuropsych testing was below normal. That’s the beauty of neuropsych testing,” he explained. “Based on reaction time and memory, we can measure on a computer, and he was below his baseline. That saves [Mysterio] from causing further injury from the concussion."

It was also confirmed that Mysterio will not return to in-ring action until he is at baseline and passes an exertion test. To be determined at baseline, Mysterio must pass the aforementioned impact/neuropsych test later in the week. Only then will he be permitted to undergo exertion testing.

WWE.com’s source estimated that the former WWE Champion “will probably be taking [the impact test today] if he’s still symptom-free, or later on this week.”

Stay with WWE.com for further updates on Mysterio’s condition.