In his first season at Old Trafford, Dutchman Van Gaal has led United to third in the Premier League despite injuries to a host of players.
Ferguson this week described Van Gaal as "a great coach" who "will do well".
"He has belief and I'm happy with that," said Van Gaal, 63. "Then you can work in an easier way."
United have suffered more than 40 injuries in the five months since Van Gaal took charge.
They are set to be without Daley Blind, Marcos Rojo, Luke Shaw, Marouane Fellaini and Ander Herrera for the Boxing Day match against Newcastle United at Old Trafford.
Ferguson is now a United director after stepping down in 2013, having won 38 trophies during his 26-year reign.
"You hope that he shall support you," said Van Gaal. "He showed a lot of confidence and belief in me and that I need as a coach.
"As manager of Manchester United, you need belief and support of managers such as Sir Alex.
"But it is also a pressure because he believes in you and it gives you that pressure that you have to get results."
Van Gaal revealed he has given his players Christmas Day off.
It is normal practice for United to train the day before a game and stay overnight in a hotel.
"I have given them free time," Van Gaal told MUTV. "We shall come together the next day here at our training complex."