Contracts have not been signed, but sources say the bout should be finalized in the immediate future.
UFC 248 is scheduled for March 7 in Las Vegas.
This will be Adesanya's first title defense. He won the belt by TKO over Robert Whittaker at UFC 243 in October.
Romero, a former wrestler for the Cuban Olympic team, has been an interim title challenger in the past. He has lost his past two fights, most recently by unanimous decision to Paulo Costa at UFC 241 in August.
Costa had initially been penciled in to challenge Adesanya for the title in March, but the UFC was forced to look at other options after Costa underwent surgery on his injured left biceps in early October.