LAS VEGAS — Conor McGregor has come to an agreement with UFC that has moved a proposed fight with Floyd Mayweather Jr. closer to reality.

UFC President Dana White said he reached a deal with McGregor , MMA's biggest star and lightweight champion, and will now start negotiations on a mega fight with the retired Mayweather that could be worth $1 billion.

"I'm not saying the fight will happen, but I've got one side done. Now it's time to work on the other," White said.

McGregor confirmed the contract for the boxing match in a statement to Themaclife.com.

"The first, and most important part of this historic contract has now officially been signed off on," McGregor said. "Congratulations to all parties involved. We now await Al Haymon and his boxer's signature in the coming days."

White and McGregor did not announce specifics of the deal.

"If we can come to a deal with Haymon and Mayweather, the fight's gonna happen," White said.

Mayweather was in London this week and told reporters he would end his nearly two-retirement for what could be the richest payday in fight history.

"There's only one fight that makes business sense," Mayweather said. "I came out of retirement because I'm a businessman and I want to give the world what they want to see. McGregor's a fighter. I'm a fighter. This is what the fight fans and MMA fans want to see."

The 40-year-old Mayweather, one of the great pound-for-pound fighters who retired at 49-0 in 2015, has said he'd want the fight to be at either 147 or 150 pounds and be part of a Showtime pay-per-view package.

McGregor, 28, hasn't fought since he defeated Eddie Alvarez at UFC 205 in November 2016. He has no scheduled UFC fights ahead.