Reliable Portuguese site MaisFutbol claims Benfica managed to loan the striker to Forest ahead of the transfer deadline.
This will be the sixth loan of Oliveira's career at Benfica, having spent a short spell with Swansea City last season, where he scored only once, struggling to hold down a starting spot.
Despite his club struggles, Oliviera has been a regular Portugal international and was part of the Euro 2012 and 2014 World Cup squads.
Portuguese website A Bola is another to report the news that Oliveira is Forest bound.
The deal would be dependent on all the necessary paperwork being filed in time with the respective authorities, and Forest are yet to announce a deal at their end.
The 24-year-old has previously had loan spells in France with Rennes and Spain with Deportivo La Coruna.