PHOENIX, Ariz. -- Nate Diaz's return to the limelight got off to a precarious start, as the popular and outspoken UFC lightweight was a noticeably absent presence from Wednesday's UFC on FOX 13 open workouts event at Phoenix's U.S. Airways Center.

As one of the four featured fighters on the Dec. 13 card, Diaz (17-9) was scheduled to appear at the fan event alongside headliners Junior dos Santos and Stipe Miocic, and upcoming opponent, Rafael dos Anjos. All three other fighters showed. Diaz was expected to as well, however he never did.

UFC representatives did not offer an official reason for Diaz's absence. Diaz is currently scheduled to appear before reporters at Thursday's UFC on FOX 13 media day.

Diaz's fight against dos Anjos will be his first in over a year, following a lengthy and self-imposed hiatus over a contract dispute with the UFC. The 29-year-old Stockton native was removed from the promotion's official rankings in May after officials deemed him inactive.

Diaz ultimately announced his return this past September, agreeing to fight dos Anjos under the terms of his old contract. His name was re-entered into the rankings, and he now stands at No. 14.