Mourinho confirmed Sanchez – left on the bench in Bern and without a goal in four games this season – would return on Saturday.
"Sanchez plays tomorrow," the Portuguese tactician told UK newspapers on Friday.
"Because Martial played 90 minutes [against Young Boys] and Sanchez played zero."
United have claimed three straight wins after a slow start to the season, but still sit eighth in the Premier League.
Mourinho believes his team will be better this campaign than they were last, when they finished a distant second to Manchester City.
"I am not saying we are going to have more points than last season because last season we collected a very acceptable level of points," he said.
"I think we are going to be a better team. We are going to play better than we did but I think it's going to be a very difficult season. Not just for us, also for the others."