The event, expected to emanate from the MGM Grand Garden Arena, will likely be UFC 130.
That event is also likely to feature a second heavyweight tilt, this one pitting fast-rising Stefan Struve against Travis Browne.
The Nelson-Mir fight was first reported by online sports book BetUS.com.
Nelson had been put on the shelf by the UFC as he attended to contract issues brought about by a deal he signed prior to joining the UFC. Those issues have reportedly been resolved, paving the way for the bout.
Mir (14-5) is coming off a UFC 119 knockout win over Mirko Cro Cop.
Meanwhile, Nelson (15-5) will be hoping to rebound from a UFC 117 unanimous decision loss at the hands of current No. 1 contender Junior dos Santos.
The addition of Mir to the card also seems to preclude him from coaching season 13 of the Ultimate Fighter. In late 2010, UFC president Dana White told MMA Fighting that Mir and Brock Lesnar were potential candidates to coach the show, but talks between the UFC and Lesnar on the possibility never panned out.
The night's other heavyweight bout will feature two fighters trying to work their way into the title picture.
The 22-year-old Struve (21-4) tries to continue his forward momentum coming off a first-round win over Sean McCorkle at UFC 119. Browne, unbeaten at 10-0-1 fought to a controversial draw against Cheick Kongo at UFC 120.