The Argentina international set a new British transfer record when he joined the Red Devils for a staggering £59.7 million fee from Real Madrid during the last transfer window.
His sale raised some eyebrows at the Bernabeu, with Di Maria having played a pivotal role for Los Blancos as they claimed a 10th European crown in May when they beat city neighbours Atletico Madrid 4-1 in the UEFA Champions League final.
But the 26-year-old felt he needed a change of scenery after four years in Madrid, and has accredited Van Gaal for selling United to him, insisting he will strive to return the club to their former glory.
He told Perform: “Van Gaal was really important for me, in order to come here. [He] was one of the first who spoke about bringing me here.
“The coach always has the last word about the players he wants. I am really grateful to him because, thanks to him, I am now playing for United.
“I keep trying to improve every day and for that reason I wanted to come here to United. I needed to change my life. I will try my best to play the right way. I will try my best every match and show my arrival at Old Trafford was worth it.
“Manchester United are trying to grow. We already know we didn’t start the Premier [League] in the right way but those things always happen in football.”
Meanwhile, new United team-mate Radamel Falcao has claimed he tried to convince Di Maria to join him at Monaco.
Falcao left the Principality for the Theatre of Dreams on transfer deadline day after a season-long loan was agreed between the two clubs.
The Colombia international made his debut for the English giants in the 4-0 win over QPR on Saturday as a substitute to line up alongside Di Maria in attack.
But the on-loan Monaco striker has revealed he failed to tempt the former Real winger into making the switch to Stade Louis II last month
Falcao told Fox Sports: “He’s a key player, compliments are short in order to describe him. When I was at Monaco I tried to get him to join me there.”