Contracts have not been signed, but the 155-pound contest is expected to be shored up shortly, multiple sources told ESPN on Saturday. The UFC 286 pay-per-view is scheduled for March 18 from the O2 Arena.
Gaethje (23-4) is looking to rebound from a loss to Charles Oliveira for the UFC's lightweight title last May. The former interim champ 5-2 in his past seven appearances, and his only losses have come against two of the best lightweights of all time in Oliveira and Khabib Nurmagomedov.
Fiziev (12-1), of Kyrgyzstan, is one of the hottest contenders in the division, riding a six-fight win streak. Most recently, he knocked out former champion Rafael dos Anjos in the final round of his first main event appearance in July. He's also picked up wins over the likes of Brad Riddell, Bobby Green and Renato Moicano.
Gaethje and Fiziev are ranked Nos. 3 and 6, respectively, in the UFC's rankings.
The UFC has not announced an official headliner for UFC 286. However, it's expected to be a trilogy welterweight title fight between Leon Edwards and Kamaru Usman. Usman and Gaethje are teammates, fighting out of Denver.