Herrera featured from the bench against Burnley but picked up an injury in training ahead of the 2-1 win over Watford last week.
Rojo, on the other hand, has not featured at all since the final day of the Premier League season having sustained an injury at the World Cup.
Speaking at a press conference this morning, Mourinho noted that the pair were the only players unavailable through injury.
“There are small things but nothing important,” he said. “At this moment, Marcos Rojo is not training with the team, but Herrera is in the final phase of his recovery. Apart from them [and the suspended players], everyone is ready.”
Marcus Rashford and Nemanja Matic will also miss the game through suspension after picking up red cards against Burnley and Watford respectively.
There were concerns during the Young Boys game on Wednesday that Alexis Sanchez, who played no part at all, was carrying an injury of some kind.
Thankfully, though, United have more or less a full compliment ahead of their first game at Old Trafford in almost a month.