Poirier and Diaz verbally agreed to fight last month after ‘The Diamond’ missed out on the lightweight title against Charles Oliveira at UFC 269.
The promotion gave the fight the green light, with UFC 270 on January 22 or UFC 271 in February being potential dates for the clash.
But reports suggest the fight has been shelved for now by the UFC, despite both men agreeing to prepare for it in less than six weeks.
Judging by recent pictures on his Instagram, Poirier is still preparing for a move to 170-pounds after his physique has drastically changed over the holiday season.
Diaz mocked Poirier in a recent tweet by suggesting the promotion informed him their fight was off because Poirier “sucks”.
“I just talked to the UFC, I said ‘what’s going on with the Dustin Poirier fight, I wanna fight as soon as possible,” he wrote.
“But they said ‘Dustin sucks’ and they don’t want it sorry. Dustin you suck hope to fight soon though let’s do this.
The Stockton native last fought against Leon Edwards at UFC 263, being outpointed by the Brit after 18-months away from the cage.
Poirier’s loss to Oliveira marked the second time he has missed out on the lightweight title, having been submitted by Khabib Nurmagomedov in 2019.
Diaz and Poirier were scheduled to meet in a lightweight fight at UFC 230 three years ago, but Poirier withdrew due to injury and the fight was never rebooked.
Former lightweight title challenger Diaz has competed at welterweight since his first fight with Conor McGregor in 2016.
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The 36-year-old – who has gone 2-3 in the weight class – is without a win since outpointing Anthony Pettis in 2019.
And Poirier admitted when talking before his fight with Oliveira that he will likely fight at 170-pounds in the future.
“I’m not sure (who I could face at welterweight), we’ll see. I mean, the whole top-10 rankings system in the UFC at lightweight is tough guys,” he told RT Sport MMA.
“There’s a lot of guys on long win streaks. There’s some up-and-comers, some new guys to the mix. There’s a lot of opponents that could be my potential next opponent, so we’ll see, man.
“I don’t know when that move to welterweight will be. But I’m pretty sure, I would say I’m 90 percent sure that before everything is said and done, that I will fight at 170 pounds in the UFC.”