Mourinho has been criticised for not playing the 20-year-old, who scored twice for England during the international break, enough in United's opening four Premier League games.
But the Portuguese said Rashford's playing time compares favourably with young English players at rival teams.
"People speaking about his minutes, they are a bit confused," he said.
In his news conference before Saturday's league match at Watford (17:30 BST), Mourinho outlined his use of Rashford over the past two seasons.
He said the forward has played 5,744 minutes in 105 games in all competitions.
"Marcus Rashford is not [Liverpool striker] Dominic Solanke. He's not [Chelsea midfielder] Ruben Loftus-Cheek. He's not [Everton forward] Dominic Calvert-Lewin," said the 55-year-old.
"He's Marcus Rashford, Manchester United player, with an incredible number of appearances and an incredible number of minutes played at the highest level in the best possible competitions."