Kamaru Usman replaces Costa to face Chimaev at UFC 294, Abu Dhabi.

Two top-ranked welterweights clash in a middleweight bout.

Kamaru Usman, a former champ, seeks redemption after a title loss.

Khamzat Chimaev, a rising star, aims for future UFC gold.

Islam Makhachev vs. Alexander Volkanovski for the lightweight title.