LAS VEGAS — Saúl Álvarez’s team had the commemorative T-shirts ready. The fighter who goes by Canelo donned one moments after he had knocked out Caleb Plant to become the undisputed supermiddleweight boxing champion.

Álvarez, 57-1-2 with 39 knockouts, also wore a shiny gold crown on his head, while his handlers tried to adorn him with his various title belts: one from each of the four major sanctioning bodies; another from Ring Magazine, awarded to the publication’s top fighter in each weight class; and a second belt from the World Boxing Council. It took some effort, but eventually Álvarez’s team found room on the boxer’s 5-foot-8 frame to display all his titles.

As Álvarez, 31, posed for photographs alongside his coaches, he looked like a proud champion. The win over Plant made him the second undisputed champion currently fighting, alongside the Scottish superlightweight Josh Taylor, as well as the first undisputed champion in supermiddleweight history. He is also the first Mexican fighter to hold all four major titles in a weight class.

He also looked like a target.

The profile and payday tied to an Álvarez bout make him an appealing future opponent for serious contenders from 160 to 175 pounds, for former champions seeking one last windfall and even for nonboxers like the Ultimate Fighting Championship standout Kamaru Usman.

Boxing megastars like Álvarez usually fight twice a year, but he has fought four times since last December and says he will most likely fight again in May. He knows he has options, but says he will not ponder them until January.

“I’ll take a little rest. I deserve it,” Álvarez said at a news conference after the fight. “After that, we’ll see what happens.”

Álvarez, a native of Guadalajara, Mexico, who is now based in San Diego, has four championship belts but no promoter. As a free agent, he has the leeway to make bouts across pro boxing’s various promotional divides and the leverage to command the price he wants. His reported guarantee for the Plant bout was $40 million.

From here, Álvarez could, conceivably, move back up to light heavyweight, a division where he won a world title in 2019, to fight the winner between Artur Beterbiev of Russia and Marcus Browne of the United States, who will meet for Beterbiev’s titles on a Top Rank show in December.

Or he could take a third fight with the middleweight champion Gennadiy Golovkin, with whom Álvarez has shared a pair of close, entertaining fights. Their first bout, in September 2017, ended in a draw. Their second, a year later, was a majority decision win for Álvarez. Those two fights generated a combined 2.4 million pay-per-view buys, and the prospect of a trilogy motivated the streaming service DAZN to sign Golovkin.

Álvarez fought six times on DAZN, first under his now-terminated contract with Golden Boy Promotions and later as a free agent in a series of one-off bouts. He returned to Showtime’s pay-per-view platform for the Plant bout, and the broadcaster hopes to leverage its ties with the Premier Boxing Champions managerial outfit to lure Álvarez back. David Benavidez, a former supermiddleweight champion, fights under the P.B.C. banner, as does Jermall Charlo, a middleweight champion open to moving up a weight class.

“We’re optimistic we’ll be able to continue the relationship,” Stephen Espinoza, president of Showtime Sports, said before the fight.

Álvarez’s allure to promoters and broadcasters is clear. In addition to his pay-per-view numbers, he attracts ticket buyers. In May, more than 73,000 spectators filled AT&T Stadium in Arlington, Texas, and watched him break Billy Joe Saunders’s face in a world title bout. On Saturday, a capacity crowd of 16,586 came to the MGM Grand Garden Arena to see him school Plant.

Those numbers also attract interest from other fighters, who recognize that an Álvarez bout is likely to bring a career-high payout.

After dispatching Marcos Hernandez with a highlight-reel, bolo punch knockout in the co-main event, the former supermiddleweight champion Anthony Dirrell mused about becoming Álvarez’s next opponent. If he cannot secure that fight, he said, he will retire.

“I’m 37 years old. If I can’t fight for something, I’m fighting for nothing,” he said at a news conference. “I’m getting too old for this, man.”

And after winning a decision over Colby Covington to headline U.F.C. 268, Usman, a 170-pound mixed martial arts champion, talked openly about fighting Álvarez in a boxing match.

“I want to do something that scares me,” Usman told reporters after his fight, referring to a match with Álvarez. “Pound-for-pound M.M.A., pound-for-pound boxing, that scares me. I’m down for those challenges. Who in the world wouldn’t want to see that?”

ESPN’s “SportsCenter” even ran a tale-of-the-tape graphic, while anchors emphasized that Usman is taller, with a longer reach, than the boxer.

Height and reach alone are not enough to solve Álvarez. Sergey Kovalev, who is 6 feet, can attest to that reality. Álvarez knocked him out in 2019. So can 6-3 Callum Smith, who lost a 12-round decision to Álvarez last December. And now, after an 11-round dismantling, so can the 6-1 Plant, who before Saturday had never lost as a professional.

But the potential payday makes sense. Official payouts for U.F.C. 268 are not yet public, but Usman made a $500,000 guarantee for his first bout with Covington. That figure most likely grew after sponsorship, performance and pay-per-view bonuses, but it did not approach Álvarez opponent money.

Plant’s reported guarantee for the Álvarez fight was $10 million.