UFC officials confirmed the news to ESPN.com, following initial reports out of Brazil. The UFC has yet to announce whether dos Santos will be replaced.
The heavyweight bout was supposed to headline the televised UFC Fight Night event on May 31 at Ibirapuera Gymnasium. Additionally, finalists from the current season of "The Ultimate Fighter: Brazil" are scheduled to appear on the main card.
Miocic (11-1) is looking to extend a two-fight win streak, as he's beaten Roy Nelson and Gabriel Gonzaga in his last two trips to the Octagon. Meanwhile, dos Santos (16-3) will have to wait to come back from a TKO loss to UFC champion Cain Velasquez in October.
The heavyweight contest was originally slated as the co-main event at UFC 173 on May 24 in Las Vegas, but eventually landed on the May 31 card.