He explained during his recent appearance on "The MMA Hour:"
"Let me tell you. It was always the plan to do one more at least. But, you don't want to just do it to do it. Like, if I watch UFC and I see something, I'm like, ‘Fuck man, I miss that.' The feeling is, like you see all of these guys, well some, not all of these guys, especially like the real warriors man, they stick around a lot of time longer than they should. It's not even about the attention, it's not about that. It's that feeling of fighting in there. It's really something man. That's why I think fighters, you know, post-fighting they turn to drugs and they turn to this and turn to that because they are missing something. They need that high, you know what I mean? It's such a high. Like when you win or have a battle in there, or whatever."
His decision to walk away from the sport seemingly popped out of nowhere, revealing that he never had a timetable for his final decision, saying it was through a casual talk with a friend at Newsday that resulted in the impromptu announcement :
"I was talking to my buddy Mark and he wanted to do a story about how I was feeling and that the word was out about my health. So it started with me and him just bullshitting because I know the guy, and then it turned into kind of like my retirement piece. And it's cool, listen, it's all good because I meant everything I said and, you know, it's not like I set out to do that. It wasn't my mission that day to wake up and say, ‘You know what, today I walk away."
Serra recently underwent rib surgery after it was discovered he was suffering form thoracic outlet syndrome -- a "disorder Matt describes as "weird" -- in which his collarbone and his first rib was compressing a vein restricting blood flow to his biceps and other areas of his body.