Dan Hardy fell off the card due to injury late Thursday with Jordan Mein quickly agreeing to take his place against Matt Brown.
UFC officials again acted swiftly, enlisting T.J. Dillashaw to step in for Rivera.
Dillashaw (7-1), like Mein, is coming off of a victory at last weekend’s UFC 158: St-Pierre vs. Diaz. He has also agreed to make the quick turn to fight on the April 20 fight card in San Jose, Calif.
His UFC 158 victory over Issei Tamura put Dillashaw on a three-fight winning since coming up shy in his bid to win The Ultimate Fighter 14.
The fight with Viana is an important one for both fighters. Viana is undefeated at 7-0 and has won both of his fights in the Octagon.
Whoever wins this bout will receive a big boost in credibility as both men try to claw their way into the title picture.