According to Dave Meltzer, Samoa Joe suffered a concussion during Monday night's episode of RAW. As you may recall, that came after he took a dive to the outside of the ring and only grazed Seth Rollins (which resulted in him landing on his head).
During the commercial break, a ringside trainer decided to send Joe to the back and he was evaluated backstage while Kevin Owens, Rollins, and Buddy Murphy called the rest of the match on the fly.
Meltzer adds that Joe's concussion is now being monitored through WWE's usual protocols. It's unclear how long he'll now be out of action but a concussion can take days, weeks, or sometimes even months to recover from.
We'll keep you guys updated as we learn more.