Julio Cesar Martinez will face a new opponent on October 23 after Maximino Flores has tested positive for COVID-19.

The WBC flyweight titleholder Martinez (16-1, 12 knockouts) will face Moises Calleros (33-9-1, 17 KOs) on the DAZN card, which will take place at Azteca Studios in Mexico City, Mexico, a source at Matchroom Boxing USA confirmed to The Ring.

Callero, 31, of Monterrey, Mexico has won five straight since losing back to back fights to championship-level fighters Ryuya Yamanaka (in WBO minimumweight title challenge) and Jose Argumedo in 2018. Callero appears to have missed out on an opportunity to be rated at 112 pounds by the WBO, when he came in nearly four pounds overweight for his regional title fight last September against Christian Eduardo Bacasegua. Callero’s last fight came in February, when he won a six round decision against Javier Romano on the undercard of Pedro Taduran’s IBF minimumweight title defense against Daniel Valladares.

Martinez, 25, of Mexico City won the title last December with a stoppage of Cristofer Rosales, and then defended it against Jay Harris in February.

Though Calleros was not rated by the WBC at the time the fight was made, the sanctioning body has approved the fight as a title defense due to the “extreme circumstances” due to the pandemic, a Matchroom source tells The Ring.

The good news for the card is that another fight which had been in danger – Ring/WBC junior bantamweight titleholder Juan Francisco Estrada defending against Carlos Cuadras – will go on as scheduled. It had been reported this week by Jake Donovan that Cuadras had failed a COVID-19 test, but that his team had come back negative, which made them wonder if the result had been a false positive.

“He retested and that came back negative,” the Matchroom source tells The Ring.

The third champion on the Superfly-like card is Roman “Chocolatito” Gonzalez, who will make a mandatory defense of the WBA junior bantamweight title against Israel Gonzalez.

“Chocolatito” Gonzalez (49-2, 41 KOs) will be making the first defense of the title he won in February with a stoppage of Khalid Yafai, while the challenger has fought twice for world titles before against Yafai and Jerwin Ancajas.