The former featherweight and lightweight champion, who hasn't fought in MMA since winning the 155-pound belt in November 2016, took to Instagram to celebrate his placement at No. 4 on the Forbes list of the world's highest-paid athletes for 2017 and to add that he would have placed higher with an "agreed May 12th bout in Rio de Janeiro" before "something came up."

That fight almost certainly would have been against Rafael dos Anjos for the interim welterweight championship. It would have been an opportunity for McGregor to win a title in a third weight class -- something no UFC fighter has done. Dos Anjos, also a former lightweight champ, ended up being scheduled instead for an interim 170-pound title bout with Colby Covington, though the fight later was moved from the Rio card to this Saturday in Chicago.

McGregor won the featherweight belt in December 2015 with a 13-second knockout of Jose Aldo, then added the lightweight strap in November 2016 with a second-round TKO of Eddie Alvarez. Both belts were stripped -- the featherweight later in November 2016 and the lightweight in April -- after McGregor did not defend either. He initially took time off for the birth of his first child, then engaged in a boxing match with Floyd Mayweather last August.

The "something" that came up and scuttled McGregor's return presumably was the April bus attack that took place during a UFC 223 media day event in Brooklyn. Two fighters were injured by broken glass and three bouts were canceled. McGregor faces three charges of misdemeanor assault and one count of felony criminal mischief and is due in court June 14.

McGregor placed fourth on the Forbes list, behind Mayweather and soccer stars Lionel Messi and Cristiano Ronaldo. The Irishman's earnings for 2017 -- all from the Mayweather fight -- were estimated at $85 million, which Forbes characterized as "more than five times his previous biggest check."

A UFC spokesman said the fight promotion had no comment on McGregor's post.