For the 2nd time this year, a UFC main event featuring Tony Ferguson has been called off. In April, Ferguson had to pull out of his UFC on FOX 19 showdown with Khabib Nurmagomedov due to a lung problem. Khabib remained on the card against Darrell Horcher, but lost his headlining status. This time around, with Ferguson set to fight Michael Chiesa at UFC Fight Night 91 in Sioux Falls, South Dakota, Chiesa had to withdraw after suffering a ruptured disc. Much like Khabib back in April, Ferguson won't be the main event anymore, and he will end up fighting a UFC newcomer.