Cunha, 23, is at the top of a shortlist of forwards drawn up by the club to strengthen the squad as United have stumbled out of the gates in the Premier League, losing their first two matches and sitting dead last in the table.
Sources added that Cunha is keen to join United to increase his playing opportunities as he tries to get into Tite's Brazil squad for the World Cup in November.
With the ability to play as a lone striker, alongside another forward or in wide positions, Cunha fits the profile of player that United manager Erik ten Hag is looking for.
However, he still has four years left on his contract at Atleti after moving there from Hertha Berlin a year ago for €30 million. With Atletico looking to reduce their wage bill and save money, they could nonetheless be willing to let him go for the right fee -- between €40m-€50m, according to sources.
Cunha has sevens caps for Brazil and has been used mostly as a sub during his first season in LaLiga with 29 appearances, six goals and four assists at the Wanda Metropolitano.
Atleti manager Diego Simeone has plenty of forwards at his disposal with Alvaro Morata, Joao Felix, Antoine Griezmann, Angel Correa and Cunha, who came on in 83rd minute of Monday's 3-0 win over Getafe.