A Bola says Sporting have accepted a £50 million offer from United for the teenage winger.
United had pushed to take Quenda immediately, however he will spend the remainder of the season in Lisbon before moving to England in June.
United had been following Quenda since before Ruben Amorim's move from Sporting to the English giants.
The teen is viewed as ideal for Amorim's 3-4-3 system.