ARLINGTON, Texas – Jermell Charlo simply doesn’t believe Brian Castano.

The unbeaten WBO junior middleweight champion postponed their rematch for nearly two months in mid-February because he suffered a slight tear to his right biceps while sparring with Terrell Gausha. That injury required rest, not surgery, which was why Castano was able to return to training sooner rather than later.

Charlo has maintained all along that Castano was out of shape, not injured, and wanted to buy time to properly prepare himself for their second fight.

Showtime will air their immediate rematch Saturday night as the main event of a three-bout broadcast from Dignity Health Sports Park in Carson, California (9 p.m. ET; 6 p.m. PT). Castano, 32, and Charlo, 31, initially were supposed to fight again March 19 at Crypto.com Arena in Los Angeles.

Castano acknowledged he wants to punish Charlo for essentially calling him a liar. Nevertheless, Charlo considers footage he has seen of Castano training soon after their second 154-pound title unification fight was postponed as all the evidence he needs to prove what he has said is true.

“I mean, he was still in the gym, running,” Charlo said recently. “He was still swinging that arm. If you got a bicep tear, let’s break that sh!t down. Y’all follow him, y’all watch him. Y’all watch him more than I am. That motherf----- got a bicep tear and he outside running, swinging the arm, acting like he punching with one arm. Come on – stop the bullsh!t! Something ain’t right. Something ain’t right with these people.”

Castano’s handlers supplied medical documentation to the WBO as proof that he was injured. Charlo contended, though, that he has not seen those documents.

“Nah, I never got to see no paperwork or nothing,” Charlo said. “They cap, man.”

Their disagreement notwithstanding, Buenos Aires’ Castano (17-0-2, 12 KOs) and Houston’s Charlo (34-1-1, 18 KOs) will get another opportunity Saturday night to settle what was left unresolved July 17 at AT&T Center in San Antonio.

Their closely contested fight resulted in a controversial split draw last summer.

Judge Steve Weisfeld scored Castano a 114-113 winner of that “Showtime Championship Boxing” main event. Nevada’s Tim Cheatham credited Castano and Charlo for their work similarly, and scored their 12-rounder a draw, 114-114.

Puerto Rico’s Nelson Vazquez curiously scored their fight 117-111 for Charlo, who won nine rounds on his scorecard.

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