Jason and Andrew Moloney were aiming to make Australian boxing history this week with two major wins headlining separate fight cards at the MGM Grand casino.

The fairytale result was dashed on Tuesday when Andrew lost his WBA super-flyweight world title in a close unanimous points decision against Texan fighter Joshua Franco.

"I'm ready to go," Jason told AAP on Wednesday.

"We didn't come to Las Vegas for two losses and I am ready to avenge his loss and take a huge step forward in my career toward getting a shot at a world-title."

Jason and Baez will fight over 10 rounds in their non-title bantamweight bout on Thursday (10am Friday AEST).

Baez was brought in as a replacement two weeks ago after a medical check discovered Jason's original opponent, Colombian-born Oscar Negrete, had a detached retina.

The 175cm-tall Baez fights one weight division up as a super bantamweight and has a 10cm height and 4cm reach advantage over Jason.

Baez will also have a weight advantage with the Mexican failing to make the 53.42kg limit on Wednesday. He came in at 53.66kg but was not forced to shed the extra grams.

Melbourne-born, Kingscliff-based Jason came in just under at 53.39kg.

"It was pretty disappointing," Jason said.

"This is professional boxing and you should be professional and make the contracted weight, but that little bit of weight is not going to help him in the ring.

"If it was a world-title they would definitely make you lose that weight, but unfortunately with the coronavirus thing and boxers not having as much notice to fight as they usually would they are being a little bit lenient."

The fight cards are held in a "bubble" at the MGM in an attempt to protect the boxers from COVID-19.

The boxers live, train, undergo regular COVID-19 testing and fight in the cordoned off section of the casino complex.

The bouts do not have spectators in attendance but are televised on Fox Sports in Australia and ESPN in the US.

Andrew was taken to hospital for a precautionary check-up after Tuesday's loss but was given the all-clear.

He was knocked down in the 11th round and suffered a cut above his left eye in the fight that two of the three judges gave to Franco by just one point.

"It was hard to watch Andrew lose like that because I know how hard he worked to win the title and get over here and be where we are, but I have to numb myself to that and move on," Jason said.

Australian Associated Press