Michael Phelps attends the 2016 MTV Music Video Awards at Madison Square Garden on August 28, 2016 in New York City.
Dimitrios Kambouris—2016 WireImage
August 30, 2017 4:26 PM EDT

It’s been less than a week since Conor McGregor faced Floyd Mayweather in the boxing ring, but the mixed martial artist already has another challenger lined up to battle him in a meeting of world-class athleticism. And this time, the popular Irish fighter is being asked to step outside the ring.

Swimmer Michael Phelps, the world’s most decorated Olympian, just threw down the gauntlet on Twitter, extending a challenge to McGregor.

“All of this talk… should we race as well?” Phelps asked on Twitter.

McGregor stepped outside of his lane to compete against Mayweather over the weekend in the much-hyped boxing match. McGregor had never boxed professionally before, focusing on his career with the UFC. Meanwhile, Phelps himself has recently had some unconventional competitors in the water: he took to the open ocean this summer to race a (simulated) shark.

The Internet is, of course, intrigued by this unexpected potential match-up. With ringside seats for the Mayweather-McGregor match running a hefty $10,000 a pop, many are also seeing the dollar signs for both athletes if they should choose to move forward with the stunt set-up.

McGregor, for his part, has not yet responded to Phelps’ challenge.

Write to Raisa Bruner at raisa.bruner@time.com.

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