Julio Cesar Martinez has been forced to withdraw from a fight for the second time since late in July.

Matchroom Boxing announced Wednesday afternoon that Martinez has pulled out of his December 19 fight against Francisco Rodriguez due to an undisclosed illness not related to COVID-19. Martinez-Rodriguez, a 12-round fight for Martinez’s WBC world flyweight title, was supposed to be the co-feature on the Canelo Alvarez-Callum Smith undercard at Alamodome in San Antonio.

Like Alvarez, Martinez is trained by Eddy Reynoso.

Mexico’s Rodriguez, the number two challenger for Martinez’s championship, will not fight someone else on the undercard December 19. Matchroom instead could reschedule the 112-pound title bout between Martinez (17-1, 13 KOs, 1 NC) and Rodriguez (33-4-1, 24 KOs), a former IBF/WBO 105-pound champion.

Matchroom also announced Wednesday that super middleweight prospect Diego Pacheco (10-0, 8 KOs) has been forced to withdraw from his fight on the Alvarez-Smith undercard due to an undisclosed illness.

The 25-year-old Martinez most recently dominated Mexico’s Moises Calleros (33-10-1, 17 KOs), whom Martinez stopped in the second round October 23 in Mexico City. Calleros replaced countryman Maximino Flores as Martinez’s opponent on short notice because Flores (25-4-2, 17 KOs) reportedly contracted COVID-19.

Martinez previously was supposed to headline a DAZN card August 15 in downtown Tulsa, Oklahoma.

His title defense against Puerto Rico’s McWilliams Arroyo was scrapped late in July, when Martinez came down with a respiratory tract infection. That led to Jessica McCaskill and former undisputed women’s welterweight champ Cecilia Braekhus, whom McCaskill upset by majority decision, headlining that August 15 card.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.