Four fighters, including former UFC light heavyweight title challenger Thiago Santos, have tested positive for banned substances following the first half of the 2023 PFL season.

According to MMA Fighting, Santos as well as fellow UFC veteran Krzysztof Jotko failed drug tests after making their promotional debuts at PFL 1 last month.

Santos lost to 2022 PFL champion Rob Wilkinson via unanimous decision in the co-main event while Jotko suffered a split decision defeat to Will Fleury.

The other fighters to fail drug tests were heavyweights Bruno Cappelozza and Rizvan Kuniev. They came out on top in their fights at PFL 2 last month with Cappelozza and Kuniev defeating Matheus Scheffel and Renan Ferreira respectively.

At this time, it has not been disclosed what the substances were nor the length of the suspension each fighter will face.

It's also unclear how the promotion will handle the situation going forward with all four fighters now out for the remainder of the 2023 season. Santos was set to face Mohammad Fakhreddine at PFL 4 on June 8 while Jotko was scheduled to fight Ty Flores in the same Atlanta card.

Cappelozza and Kuniev didn't have any fights booked at the time of the fight.

One thing is for sure — this news is a big blow for PFL president Ray Sefo and the rest of the promotion, especially as Thiago Santos and Krzysztof Jotko were relatively high-profile pickups for them.

And the saga is not over just yet as there could be more PFL fighters failing drug tests in the very near future.