Dustin Poirier has been warned that he needs to improve his conditioning if he is to beat Nate Diaz in a prospective bout.
The former lightweight title contenders are locked in negotiations over a fight to happen later this year in what would be Poirier's move up to welterweight.
Diaz is flirting with leaving the promotion, with sources indicating that he is looking to take a boxing match against Jake Paul later in the year after his last UFC fight.
