The Red Devils were linked with a loan move for the Frenchman after they failed to sign their primary attacking target, Jadon Sancho.
United ended up having a busy transfer deadline day, brining in Edinson Cavani, Alex Telles, Facundo Pellistri and Amad Traore, but a deal for Dembele could not be done.
Dembele is considered surplus to requirements at Barcelona under new manager Ronald Koeman, who was hoping to raise funds for new signings by getting the 23-year-old off the wage bill.
A deal was agreed to sign Lyon forward Memphis Depay and negotiations were ongoing to bring in Manchester City defender Eric Garcia, but both were shelved as Demeble could not be sold, according to the Evening Standard.
Barca had agreed a £22.5m deal for Depay and the Dutchman was ready to make the move to the Camp Nou, but his move was dependent on Dembele’s exit.
With Pep Guardiola bringing in Ruben Dias and Nathan Ake this summer, a deal for Garcia was expected to be completed before the deadline, but was impossible without further departures from Barca.
It has not been quite the major squad overhaul expected at Barcelona this summer under Koeman, with Miralem Pjanic, Trincao, Segino Dest and Matheus Fernandes the major signings.