MANILA, Philippines -- The Games and Amusements Board (GAB) on Wednesday announced that it will conduct an investigation into Filipino boxer John Riel Casimero, who was alleged to have violated medical guidelines ahead of his next fight.

Casimero, 33, was scheduled to defend his WBO bantamweight title against Paul Butler at the Echo Arena, Liverpool, England on April 22.

However, it was discovered by the British Boxing Board of Control that Casimero used a sauna ahead of the bout -- which is not allowed in the United Kingdom. He was also observed to have had "an alarming reduction in weight."

• FULL STORY: Casimero broke weight-loss rules ahead of title fight, says British boxing body

GAB chairman Baham Mitra has now instructed the agency's boxing and other contact sports division to conduct an independent investigation into the matter.

"As the country's pro boxing regulatory agency, we strongly condemn and discourage the commission of any illegal acts or violation of boxing rules," said Mitra.

"We will surely look into this and summon Mr. Casimero and his team to shed light on the issue," he added.

The World Boxing Organization has written a show-cause order dated Tuesday and addressed to Egis Klimas, Casimero's manager. Casimero has 48 hours to show cause as to why his WBO title should not be declared vacant.

The British boxing board strictly forbids boxers from using saunas to lose weight, and fighters who break or are suspected of breaking this rule "will be refused permission to box without exception."

Another Filipino fighter, Jonas Sultan, will replace Casimero in the bout against Butler which will now be for the interim WBO bantamweight belt.

This is the latest in a string of challenges for Ormoc City's Casimero, who won the WBO belt from Zolani Tete in November 2019 and has since defended it twice. His most recent title defense was a split decision win against Cuban legend Guillermo Rigondeaux in August 2021.

He was supposed to defend against Butler in December 2021 in Dubai, but missed the weigh-in. It was reported that he suffered from gastritis, preventing him from showing up to the bout.