Canelo Alvarez’s longtime goal of becoming undisputed boxing champion is further from reality than ever since he won his third 168-pound title in May.

Boxing’s top star was on the verge of a deal to meet Caleb Plant on Sept. 18 in Las Vegas — a PBC on Fox pay-per-view — a pact that was in the works for weeks. But at the 11th hour, talks have broken off over disagreements in the contract, multiple sources told ESPN on Tuesday. The contract was passed back and forth between Canelo’s team and Al Haymon’s Premier Boxing Champions over the weekend, sources said, and after multiple edit requests, the deal collapsed over the stalemate.

Talks could be revisited, sources said, but time is running out if Canelo plans to fight on Mexican Independence Day weekend as he traditionally does. If he moves on from a fight with Plant, who holds the only super middleweight title not in Alvarez’s possession, another option is a return to 175 pounds for a title tilt with Russia’s Dmitry Bivol, sources said.

Alvarez’s team had requested a rematch clause, a concession Plant and PBC agreed to, sources said.

Canelo’s two-fight deal with Matchroom’s Eddie Hearn expired following his May TKO victory over Billy Joe Saunders, opening the door for Alvarez to seek a one-fight deal with Haymon’s team that would have earned him a career-high payday. The Mexican was set to make upwards of $40 million guaranteed, sources said, for a fight that would have been presented in conjunction with Canelo Promotions.

“I’m coming, my friend,” Alvarez (56-1-2, 38 KOs) said in the ring after he fractured Saunders’ orbital bone, a coldly delivered warning to Plant.

The deal — negotiated by Alvarez’s reigning trainer of the year, Eddy Reynoso — would have marked Alvarez’s return to pay-per-view, a platform he has headlined on nine times since his fight with Shane Mosley in 2012. Those bouts include a megafight with Floyd Mayweather in 2013 and a pair of matchups with his bitter rival, Gennadiy Golovkin.

Now, Alvarez could return to DAZN, the platform that has streamed his last six fights, beginning with a December 2018 win over Rocky Fielding.

Following the rematch with GGG in September 2018, Alvarez linked up DAZN on a 11-fight, $365 million deal. But after just three fights together, a dispute led to a legal battle between the fighter and DAZN (along with then-promoter Golden Boy). The spat was settled, and Alvarez became a network and promotional free agent. His past three fights were promoted by Hearn on DAZN.

Delivering Canelo to Fox would have been a coup for Haymon, whose three-year deal with the broadcast platform expires later this year but includes a network option for a fourth year, per sources. A fight between Alvarez and Plant would have been sandwiched between two other major PPV fights: Manny Pacquiao-Errol Spence Jr. on Aug. 21 (Fox) and Tyson Fury-Deontay Wilder on Oct. 9 (ESPN+/Fox).

There was reason to believe Alvarez would link up with PBC for multiple fights. If Canelo plans to remain at 168 pounds — he’s ESPN’s No. 1 super middleweight — Haymon offers the best available opponents. There’s Jermall Charlo, the undefeated, brash-talking middleweight champion who has long pushed for a meeting with Alvarez.

Haymon also advises David Benavidez, the former 168-pound titleholder who many in the industry believe will present the toughest challenge for Alvarez with his relentless volume punching and enormous size. And don’t count out a future fight with Spence. He currently campaigns at 147 pounds but owns a large frame; he figures to move up to 154 pounds next year.

For now, Alvarez is left to cement an opponent for Sept. 18, whether that means circling back to Plant or finding someone else. Alvarez had actually already begun preparations for Plant (21-0, 12 KOs) at his gym in San Diego. Alvarez’s two dates have traditionally been Cinco De Mayo weekend and Mexican Independence Day weekend. Yet he also fought in December, a decision win over Callum Smith to claim the unified 168-pound championship, and stayed busy with a third-round TKO of Avni Yildirim in February. If he fights on Sept. 18, it will be Alvarez’s fourth fight in nine months. Superstar boxers routinely compete just twice a year, and that used to be the case for Canelo.

Canelo is ESPN’s No. 1 pound-for-pound boxer. He claimed titles at 154 pounds, 160 and 175 and has won every fight since his draw with GGG in 2018.

No matter whom he fights, Alvarez is a box-office bonanza, but he hasn’t been able to flex his proverbial muscle on PPV in three years. His last three bouts were offered on pay-per-view, but that wasn’t a major revenue driver since they were only available for substantially less money as part of a monthly subscription to DAZN.

Canelo’s two fights with Golovkin both generated more than 1 million PPV buys; his 2013 matchup with Floyd Mayweather pushed past 2 million.

Plant, of course, isn’t nearly as well-known as either of those stars, but there’s reason to believe he would make for a commercially viable foil for Alvarez. The 29-year-old has headlined on Fox in three consecutive fights and isn’t shy when it comes to boasting about his talent and dedication to the sport. A self-professed gym rat, the Nashville native possesses one of boxing’s best jabs. He also owns lightning-quick hands and excellent footwork to go along with a powerful frame for the 168-pound division at 6-foot-1. What Plant has lacked: top-flight opposition. His best opponent was Jose Uzcategui in Plant’s title-winning effort. He’s also encountered hand issues, including in his most recent victory.

The fight with Alvarez would have seen Plant rise several levels in class. He, too, was set to earn a career-high payday, a package worth more than $10 million, sources said. While Plant hasn’t been tested, he’s looked the part in all his fights and is rated No. 3 by ESPN at 168 pounds. One attribute Plant certainly isn’t lacking ahead of his career-defining night: confidence.

“He’s looked human in some of these bigger fights,” Plant said in May. “He’s been fighting these U.K.-level guys and that’s cool, but as far as him fighting the top — Floyd Mayweather, Erislandy Lara and Gennady Golovkin [twice] — he’s 1-3.” Alvarez is actually 3-1 in those fights, but the draw with GGG and win over Lara were disputed decisions.

Now, Plant might not have a chance at all to prove Alvarez is just that — another man.