The 22-year-old has been in impressive form for his Portuguese club during the 2021-22 campaign, scoring 34 goals and registering four assists in 41 appearances in all competitions.
Meanwhile, he has netted 48 goals and registered 16 assists in 85 outings since making the move to the Eagles from Almeria in September 2020.
The Red Devils have allegedly identified Nunez as a leading transfer target, with the Uruguay international coming to the attention of a number of leading European clubs with his form this season.
Benfica are in a strong position when it comes to the striker's future, as he still has more than three years left to run on his contract with the club.
Incoming Man United boss Erik ten Hag will be backed during this summer's transfer window, but a lack of Champions League football for next season will see the club take a financial hit.
As a result, £120m has allegedly been set aside for new signings, and the 20-time English champions are believed to want a new centre-back, midfielder and wide player, in addition to a new forward.
Cristiano Ronaldo, though, is expected to stay at the club this summer despite the widespread speculation surrounding his future, with the Portuguese recently paying tribute to Ten Hag's work at Ajax.
Martial will be back at Man United this season following the completion of his loan spell at Sevilla, but it is unclear whether the Frenchman has a long-term future in Manchester.
Man United's struggles this season mean that they will not be present in next season's Champions League, with the club instead battling West Ham United for sixth position, which would bring a spot in the 2022-23 Europa League.
A win for the 20-time English champions against Crystal Palace on Sunday would see them claim sixth, but a draw or a defeat would open the door for West Ham, who travel to Brighton & Hove Albion on the final weekend.
Rashford, Jadon Sancho and Luke Shaw have all been back in training with Man United this week ahead of the clash at Selhurst Park, with the trio pushing to be involved in their side's final match of the campaign. body check tags ::