Assuncao had surgery to repair a fractured ankle this past December and will not be cleared to return for the March 21 card from Rio de Janeiro, Brazil.
The 32-year-old Assuncao (23-4) is on a seven-fight win streak and was slated to compete for the UFC bantamweight title before an injury. T.J. Dillashaw, who the Brazilian defeated in 2013, took his place and won the belt from Renan Barao.
Faber (32-7) has won two straight via submission and is still unbeaten in non-title fights.
The card currently features Josh Thomson vs. Gilbert Burns and Demian Maia vs. Ryan LaFlare. The report did not say if a replacement would be found to keep Faber on the card.