CARSON, California – Brian Castano has spent his past 22 rounds trying to beat Jermell Charlo.

The well-informed former WBO junior middleweight champion would advise an ambitious Tim Tszyu to gain some more experience before the unbeaten Australian contender attempts to achieve what Castano couldn’t accomplish against the fully unified 154-pound champion. Castano indicated during a post-fight press conference following his 10th-round knockout defeat to Charlo on Saturday night at Dignity Health Sports Park that Tszyu is not properly prepared for that type of difficult fight.

“He’s a great fighter, but he’s probably a little not ready for [Jermell Charlo],” Castano said. “He should face another opponent before that, even though he looked great when he beat Terrell Gausha. But this is a business, so I know he was looking [to fight] me. So, if I’m offered a fight with him in the U.S., and it makes sense, this is business and I will take it.”

The 27-year-old Tszyu is the mandatory challenger for the WBO belt Charlo won from Castano in a fantastic “Fight of the Year” candidate that Showtime televised. Tszyu stepped aside to help allow an immediate rematch between Houston’s Charlo (35-1-1, 19 KOs) and Buenos Aires’ Castano (17-1-2, 12 KOs) to take place after their controversial 12-round split draw last July 17 at AT&T Center in San Antonio.

Terrell Gausha knocked down Tszyu in the first round of Tszyu’s most recent bout, but Tszyu got up and defeated Cleveland’s Gausha by unanimous decision. Tszyu (21-0, 15 KOs) beat Gausha (22-3-1, 11 KOs) by scores of 116-111, 115-112 and 114-113 in a 12-round main event Showtime aired March 26 from The Armory in Minneapolis.

Tszyu, a son of legendary 140-pound champion Kostya Tszyu, sat ringside Saturday night to watch a closely contested title unification fight Charlo won when he knocked Castano to the canvas twice during the 10th round. He wants to challenge Charlo next, but Charlo was dismissive of defending his IBF, WBA, WBC and WBO belts against Tszyu.

Charlo already has an overdue defense of his IBF belt against Russia’s Bakhram Murtazaliev (20-0, 15 KOs). Interim champion Sebastian Fundora (19-0-1, 13 KOs) also is the WBC’s mandatory challenger for one of Charlo’s four titles.

The winner of an unscheduled elimination rematch in which number one-ranked Israil Madrimov (8-0, 6 KOs) will face second-ranked Michael Soro (35-3-1, 24 KOs) will become the WBA’s mandatory challenger for Charlo’s remaining championship.

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