Roy Nelson became the latest heavyweight to land a new opponent for UFC 146, the promotion announced Monday on its website.
On the May 26 main card, Nelson will now face Gabriel Gonzaga at MGM Grand Garden Arena in Las Vegas.
Mir replaces top contender Alistair Overeem, who was pulled from the card after failing a random prefight drug test.
Nelson, the former International Fight League heavyweight champion, has a professional record of 16-7. Since winning The Ultimate Fighter series in 2009, Nelson has struggled to find his footing in the Octagon.
He has won just two of his five most recent UFC fights.
Gonzaga, a one-time UFC heavyweight contender, returned to the promotion on Jan. 14 and registered a first-round submission victory over Edinaldo Oliveira.
He was released by UFC following an October 2010 loss to Brendan Schaub.
Gonzaga will carry a 13-6 record into his fight with Nelson.