Promotion officials announced Thursday that Aubin Mercier pulled out of the contest due to injury, and Santos later withdrew from the card as well. UFC 212 takes place on June 3 in Rio de Janeiro and is headlined by a featherweight championship showdown between Jose Aldo and Max Holloway.
Aubin-Mercier has won five of his last six UFC appearances. Most recently, the 28-year-old Canadian submitted Drew Dober with a rear-naked choke in the second round at UFC 206 this past December.
Santos, meanwhile, is unbeaten in his last 11 fights, with a draw against Norman Parke the only blemish on his record during that time. The 37-year-old is 5-0-1 in the Octagon and owns a notable victory over rising 155-pound talent Kevin Lee.