The biggest factor in Daniel Bryan's career ending early is going to be injury. He's reportedly in a physically bad way. He had the neck issue that ruled out most of 2014 and if that returns then it'll probably be a career ender. More surgery is going to finish him as an in-ring performer. The fear when he was pulled from the european tour was that the neck had indeed been re-injured. But Bryan Alvarez of Wrestling Observer Radio is now reporting it was a concussion that caused Bryan's withdrawal. That's obviously not as ominous as it could have been. But then again, take a look at Dolph Ziggler's career since he sustained a concussion while World Champion in 2013. Even when fit, Bryan is wrestling on borrowed time. You don't sustain injuries like he did and just come back the same. It is a shadow over him that isn't going away, constantly putting his WWE career in jeopardy.
