The welterweight fight was originally scheduled as the co-main event of the year-end card, which takes place at the UFC Apex in Las Vegas. Thompson-Neal will now be a five-round contest.
Edwards reportedly tested positive for COVID-19 recently, forcing him out of the matchup against Chimaev. The UFC hopes to reschedule that fight for early 2021.
Multiple injuries have kept Thompson sidelined since his win over Vicente Luque at UFC 244 in November 2019. The former title challenger is 2-2 in his past four bouts.
Neal, a rising 170-pound contender, is coming off a knockout win over Mike Perry last December. The 30-year-old is 5-0 in the UFC.
The Dec. 19 card also features a pair of marquee bantamweight clashes: Marlon Moraes versus Rob Font and Jose Aldo against Marlon Vera.