Former UFC champion Conor McGregor's return to action helped trigger a split between the league and the U.S. Anti-Doping Agency, which has been testing the league's mixed-martial arts fighters for the past eight years. McGregor announced on social media this week that he is returning to the USADA testing pool — a step the 35-year-old fighter must take before returning to the octagon for the first time since suffering a leg injury in July 2021. McGregor was expected to fight Michael Chandler in December, though the timing of their meeting has been in flux because of the testing rules.