Moises Fuentes will undergo emergency surgery following a brutal knockout loss.

An ill-advised ring return for the former strawweight titlist ended on a horrifying note, as Fuentes was knocked out by David Cuellar in the sixth round of their ESPN+ main event Saturday evening at Grand Oasis Hotel in Cancun, Mexico. A left hook by Cuellar sent Fuentes straight to the canvas, lying motionless as the referee immediately called for medical assistance.

Cuellar was in complete control of the fight, expected of the 19-year-old junior bantamweight who has rapidly emerged as a prospect to watch. Several jabs and left hooks from Cuellar in the early going caused swelling around the right eye of Fuentes, who hadn’t fought since a fifth-round knockout loss to a then-comebacking Roman ‘Chocolatito’ Gonzalez in September 2018.

The evening never improved for Fuentes, who was rocked and nearly dropped by a right hand in round three. Cuellar continued with his two-fisted attack, to the point of Fuentes’ management and even WBC president Mauricio Sulaiman—who was ringside as the sanctioning body had a regional title at stake—strongly suggesting that the corner stop the fight.

Fuentes was granted one more round, which proved to be the very wrong decision. Cuellar (20-0, 13KOs) emphatically closed the show, landing a right hand to drive back Fuentes before putting him flat on his back with a fight-ending left hook.

The bout was halted at 2:11 of round six, as any thought of a celebration quickly gave way to expressed concern for Fuentes’ health and well-being.

Fuentes was taken out of the ring on a stretcher and transported to a nearby hospital for observation. Event handlers informed that the 36-year-old from Mexico City is scheduled for emergency surgery 7:00 a.m. Sunday.

At his best, Fuentes (25-7-1, 14KOs) served an integral in the strawweight and junior flyweight division in the early 2010s. The 14-year pro enjoyed his best stretch in the early part of the decade, beginning with a 12-round, split decision win over countryman Raul Garcia to claim the WBO strawweight title. Two defenses followed, including a 5th round stoppage of former two-division titlist Ivan Calderon in October 2012 in what turned out to be the final fight of the Puerto Rican’s storied career.

Fuentes fell just short of becoming a two-division titlist himself, settling for a 12-round draw with Donnie Nietes in their March 2013 WBO junior flyweight title fight in Cebu City, Philippines. Three wins followed for Fuentes—including a TKO win over Luis de la Rosa to claim the interim WBO title—before suffering a ninth-round knockout loss to Nietes in their May 2014 rematch.

An ensuing five-fight win streak saw Fuentes add two more former strawweight titlists to his collection in back-to-back fights. Fuentes stopped countryman Oswaldo Novoa inside of six rounds in July 2015, five months before earning an upset split decision over Francisco ‘Chihuas’ Rodriguez later that December.

A stoppage win of Rommel Ansejo in April 2016 positioned Fuentes for a crack at the vacant WBO junior flyweight title, though falling miserably short in a fifth-round stoppage to then-unbeaten Kosei Tanaka in December 2016. The setback marked the start of a rough stretch, having now lost five of his last six fights to close out his career.

One fight remains, the one to return to good health and enjoy life well beyond the sport.

Jake Donovan is a senior writer for Twitter: @JakeNDaBox