On Saturday Elon Musk said that if it appears the mixed martial arts cage fight he has joked about with fellow billionaire Mark Zuckerberg begins to appear likely to happen, he will start training in earnest for the fight.

On Tuesday, Musk had tweeted jokingly he would be game to engage in a cage fight with Zuckerberg in Las Vegas while discussing Meta Platforms new Twitter-like microblogging app. Zuckerberg, who has trained in Jiu-Jitsu responded with a request to send him a location to show up to, for the fight.

Musk, in an interview on Twitter with author Ashlee Vance, who has written a book about Musk and the race to gain control of the spaceflight industry, said on Saturday, “I haven’t started training yet. So if this does happen, I will.”

While at a birthday party in Europe, Musk said the fight “might actually happen,” noting it might go badly for him if Zuckerberg chose to take the match seriously.

In the interview, Musk also noted that SpaceX would invest as much as $3 billion in the rocket Starship, whose maiden flight in April ended with the rocket exploding over the Gulf of Mexico. Environmentalists have questioned the environmental impacts of the project.

Musk noted SpaceX was actively working to develop improvements to the Starship rocket.