Ole Gunnar Solskjaer wanted to test Scott McTominay's reaction to being appointed captain for the first time in his Manchester United career.
McTominay, 24, led United for the FA Cup third round visit of Watford and scored the only goal of the game for his fourth strike of the season.
Former United manager Jose Mourinho regularly rhapsodized about McTominay's character and, after a slow start under Solskjaer, the Scotland international has become a key cog in the United side.
McTominay, Nemanja Matic, Axel Tuanzebe, Jesse Lingard, Marcus Rashford, Bruno Fernandes and club captain Harry Maguire all received the armband on Solskjaer's watch for the first time and the United manager insists McTominay is a natural leader.
"He's got great character," Solskjaer said. "Good attitude, comes in every day, does the right things, lives his life properly, wants to be the best he can be, he's not afraid to be vocal but always goes out there to give his best, never shirks a tackle, nothing.
"He's got everything a leader has to have. I just wanted to test him today, how he reacted, because he always does that anyway. I wanted to give him the armband and see if there was any change and I'm glad there wasn't."
Mason Greenwood started up front for United against Watford but struggled before he was substituted for Anthony Martial in the second-half.
The 19-year-old has only mustered three goals all season and United coaches see his role as more central, despite thriving from the right for most of last season.
"We had a front four with Dan [James], Juan [Mata], Jesse [Lingard], with Mason in front of him," Solskjaer explained. "With the licence to chop and change a little bit, find positions.
"Mason's a naturally floaty forward anyway, sometimes when you're young, staying through the middle is a challenge, and he tried to get a touch on the ball and got wide. I felt he benefited from this game, Mason."
