The injury bug has hit the UFC 176 headliner.
UFC President Dana White informed the FOX Sports 1 program of the injury, but details of what's plaguing Aldo were not revealed.
The fight between Aldo and Mendes was scheduled to headline the upcoming pay-per-view, which is tabbed to take place on Aug. 2 in Los Angeles. The bout was to be a rematch of their UFC 142 contest, which Aldo won by knockout in the first round.
A replacement to pit against Mendes for the August card was not revealed in the report.
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