Veteran boxing reporter Dan Rafael broke the news on X.

“Per source involved, Tony Yoka has suffered a back injury and is out of his fight with WBA heavyweight titlist Murat Gassiev,” Rafael wrote. “Undetermined yet if it will be rescheduled or if a modern opponent will be sought.”

No official replacement has been announced, and it remains unclear whether organizers will move quickly to find another opponent for Gassiev or postpone the bout altogether.

The contest was scheduled to headline a July 11 card at Moscow’s VTB Arena and would have been the first defense of Gassiev’s WBA “Regular” heavyweight title. The former unified cruiserweight champion has been looking to establish himself as a force in the heavyweight division after capturing the secondary WBA belt earlier this year.

For Yoka, the withdrawal is another frustrating setback. The 2016 Olympic gold medalist had been aiming to secure the biggest victory of his professional career after rebuilding momentum with recent wins following a hard stretch that included several defeats and multiple canceled opportunities.

With little more than a week remaining before the event, promoters now face a race against the clock to determine whether Gassiev will defend his title against a tardy replacement or if the fight will have to be pushed back to a later date.

On paper, it was a curious title defense from the moment it was announced. Yoka remained a recognizable name because of his 2016 Olympic gold medal, but his professional career never matched the hype. Nine years after turning pro, the 15-3 Frenchman had built his record largely against circumscribed opposition, while each of his biggest tests against Martin Bakole, Carlos Takam and Ryad Merhy ended in defeat.

The list is headlined by Usyk, the undefeated heavyweight champion, and undisputed super bantamweight king Naoya Inoue (33-0), who remains the only dynamic undisputed champion among the unbeaten titleholders.

Several other multi-title champions also remain unbeaten, including David Benavidez (32-0), who holds the WBA and WBO cruiserweight championships, and Zhanibek Alimkhanuly (17-0), the unified IBF and WBO middleweight champion.

The United States is heavily represented on the list with champions including Devin Haney (33-0), Dalton Smith (19-0), Richardson Hitchins (20-0), Shakur Stevenson (25-0), Gervonta Davis (30-0), Raymond Muratalla (24-0), Abdullah Mason (20-0), Bruce Carrington (17-0), Jesse “Bam” Rodriguez (24-0), and now Ennis.

Other undefeated titleholders include Rafael Espinoza (28-0), Seiya Tsutsumi (13-0-3), Jose Salas Reyes (17-0), Isleys Iglesias (15-0), and Collazo.

Former undisputed champion Terence Crawford also retired with a perfect 42-0 record, although he is no longer an dynamic champion.

Keeping an undefeated record becomes challenging as fighters reach championship level and begin facing the division’s best contenders. Ennis joins a select group of unbeaten world champions spanning every level of the sport, from heavyweight champion Oleksandr Usyk to minimumweight titleholder Oscar Collazo.

UFC Octagon announcer Bruce Buffer has been around the UFC for decades and has seen plenty of up-to-date countries.

Just recently, Buffer was in Baku, Azerbaijan, for the second time, which is a country he didn’t expect to go to until the UFC hosted an event.

So, as the UFC continues to go to up-to-date countries and markets, there are four places he’d like to see host a UFC event.