Conor McGregor turned the UFC world upside down in less than 140 characters Tuesday, cryptically tweeting that he has made the decision to "retire young."

I have decided to retire young.
Thanks for the cheese.
Catch ya's later.

— Conor McGregor (@TheNotoriousMMA) April 19, 2016

No one really knows what McGregor means. He may have just announced his retirement at the age of 27, or perhaps McGregor is simply sharing that he doesn't plan to fight well into his 30s. As one of the biggest stars in sports, and at the height of his earning potential, it would seem crazy for McGregor to actually retire - but he would certainly have lucrative options outside of the octagon.

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McGregor's Irish compatriot Becky Lynch suggested on Twitter that the UFC superstar should make the jump to professional wrestling and join WWE.

.@TheNotoriousMMA #ComeJoinMeBro

— Becky Lynch (@BeckyLynchWWE) April 19, 2016

McGregor wouldn't be the first MMA star to transition to WWE. "The World's Most Dangerous Man" Ken Shamrock is the best example of a success story. Shamrock came to WWE in 1997 as a former UFC Superfight Champion and became a star over a short two-year span, winning the Intercontinental title and the 1998 King of the Ring.

MMA legend Dan Severn held the UFC Superfight title and the NWA heavyweight title simultaneously in 1995, and had a short run in WWE in the late 90s. Alberto Del Rio and Shinsuke Nakamura each had short MMA careers before stepping into a WWE ring, while Brock Lesnar became the UFC heavyweight champion after his first stint as a pro wrestler.

Would McGregor work for WWE? He'd certainly be a massive draw, but would also undoubtedly clash with everyone else on the roster. McGregor has trained as a boxer and a fighter, but not as a pro wrestler - and it would be interesting to see if WWE would have McGregor remain a fighter (think Floyd Mayweather vs. The Big Show at WrestleMania) or have him actually learn how to wrestle.

There's also the challenge of his character. McGregor has one of the biggest personalities in sports, and it would almost be comical to see him in any storyline that doesn't revolve around the WWE title. McGregor's such a big star that he would have to be treated as such, but that limits who he could believably face in WWE. As a five-matches-per-year, Brock Lesnar-type of attraction, McGregor could make for some must-watch pay-per-views, but it's hard to see him working as a weekly Raw main eventer.

Alternatively, WWE could bring back the Lion's Den.