The Serbian midfielder was given extended leave so he could take a holiday after his World Cup campaign with Serbia, but rejoined the squad at the weekend.
The 29-year-old stayed in Los Angeles to train yesterday while his team-mates played in Santa Clara, but Matic was in the thick of it once again during Monday's workout.
It was a lighter recovery session for most, with this session being the first since the team’s 0-0 draw with San Jose Earthquakes at Levi's Stadium in Santa Clara on Sunday.
Alexis Sanchez made his return to match action during that game, but Jose Mourinho stressed after the game that United’s next fixture – against AC Milan in Los Angeles on Wednesday evening – would be too early to reintroduce Matic.