Ryan LaFlare told Newsday that a knee injury forced him to pull out his co-main event bout against Gunnar Nelson at UFC Fight Night 46 in Dublin on July 19.
The UFC announced the fight switch on Wednesday morning but did not indicate the nature of the injury.
LaFlare, co-owner of Long Island MMA in Farmingdale, said he expects to be out for six to nine months.
LaFlare (11-0, 4-0 UFC) is ranked No. 14 in the UFC's welterweight division. Zak Cummings replaced LaFlare on the card, which is headlined by Conor McGregor vs. Cole Miller.