The pay-per-view event is scheduled to take place at Scotiabank Arena in Toronto.
Nelson (16-3-1) hasn't fought since a first-round knockout loss to Santiago Ponzinibbio in July 2017. He was supposed to return against Neil Magny in May but was forced to withdraw from that bout due to a knee injury.
A native of Iceland, Nelson's last win came against Alan Jouban via guillotine choke in March 2017. Pending an extremely quick turnaround, this will be the first time Nelson has fought less than twice in a calendar year since 2011.
Oliveira (19-5-1) will ride a two-fight win streak into the contest, with back-to-back finishes against Carlos Condit and Carlo Pedersoli. The 30-year-old Brazilian has won six of his past seven bouts, with one no-contest in 2016.