In the meantime, Neymar continued his fine form for Barca with his third goal in two matches to condemn United to their first defeat of pre-season at FedEx Field in Landover, Maryland on Wednesday.
Neymar and Lionel Messi produced a wonderful first-half performance, the former stripping Antonio Valencia of the ball in the penalty area and finding the back of the net in the 31st minute – enough to secure back-to-back wins for new Barca coach Ernesto Valverde.
There were eight changes to the United team who started in the penalty shoot-out win over Real Madrid. Captain Michael Carrick, Marcus Rashford and Jesse Lingard were the only players to retain their positions as David de Gea, Daley Blind, Chris Smalling, Victor Lindelof, Antonio Valencia, Henrikh Mkhitaryan, Paul Pogba and Romelu Lukaku came into the XI, with Ander Herrera and Juan Mata nursing injuries.
Barca also rang the changes following their 2-1 win against Juventus. Luis Suarez, Jordi Alba, Samuel Umtiti, Nelson Semedo, Sergio Busquets and 19-year-old midfielder Carles Arena – nicknamed Maradona – were named in Valverde's line-up, which was headlined by Neymar and Messi.
United started brightly, their pace on the break through Rashford and Lingard causing plenty of problems as the former picked out Lukaku in the third minute, but the outstretched Belgian was unable to keep his effort on target.
Barca began to control proceedings as the half wore on – De Gea kept busy by Neymar, Messi and Suarez, firstly denying the latter.
Some trademark passing from Barca created space for Messi, who almost opened the scoring in the 12th minute but his low shot flashed just wide of the post.
After Pogba produced a sublime turn and shot to test Jasper Cillessen from the edge of the area, Rashford bundled his way into the area and attempted to curl the ball into the far corner but the Barca keeper was up to the task.
It was one-way traffic from that point as De Gea denied Neymar from close range but the United shot-stopper was helpless to stop the Brazil international just past the half-hour mark.
Valencia cut out a pass from Messi but he was dispossessed by Neymar, who composed himself as he turned and shot beyond De Gea.
Barca's lead could have been greater at half-time if not for De Gea after the Spain international pushed away Suarez's inventive and acrobatic strike three minutes before the break.
That proved to be the final action for De Gea, Suarez, Neymar and Messi as the quartet were replaced at the interval – Barca substituting all 10 outfield players, while Jose Mourinho made five changes.
The changes affected the fluidity and tempo of the match but United still looked dodgy in defence against a second-string Barca side.
While Anthony Martial, Andreas Pereira and Pogba had chances on goal without troubling Cillessen, United struggled defensively as Pac Alcacer played the ball through the legs of Eric Bailly before almost curling an effort past Sergio Romero.
After earning Mourinho's praise following his moment of brilliance to set up Lingard against Madrid last time out, Martial was lively out wide and United's biggest threat but he was unable to prevent defeat.