What the deuce?

Ultimate Fighting Championship (UFC) lightweight champion Conor McGregor recently proved he can hang in a sport outside his own, taking Floyd Mayweather Jr. — one of the greatest boxers of all time — 10 rounds before succumbing to a technical knockout loss against the ropes.

Watch the replay here.

So if “Notorious” can take on the best in boxing, why not challenge the top dog in swimming? Olympic gold medalist Michael Phelps was on Twitter last night proposing a super swim off, or whatever the heck you would call it, to see just how good the trash-talking Irishman can perform under water.

I kind of liked him better as a lightweight jockey.

While McGregor would probably accept the challenge, simply because he’s an amazing unicorn, the most likely scenario has “Notorious” returning to the Octagon later this year to defend his title, or perhaps settle his trilogy with Nate Diaz.

Or not.