The 23-year-old has seen his career stutter since a memorable breakthrough at Old Trafford as a teenager under David Moyes, when regularly impressing from out wide.
Januzaj saw his number of appearances dwindle upon Van Gaal's appointment in 2014, however, starting seven Premier League games before being shipped to Borussia Dortmund on loan.
Having failed to break back into United's ranks in the subsequent years, and being loaned out for a second time to Sunderland in 2016-17, the Belgium international left for Real Sociedad last summer on a permanent deal.
"I didn't have any chances, really," he told The People of his time working under Van Gaal. "I wasn't in the race [for places]. How can I say this; [Van Gaal] wasn't giving me the right signals to up my game. I was still only a young player. When you have a young player, a manager has to give them confidence.
"Let them play and grow up. Obviously, that didn't happen under Van Gaal, so it was a very difficult season for me. Before that, David Moyes had trusted me from day one. He understood I was a young player, but when Van Gaal arrived, everything changed, my progression stopped.
"For a football player, the most important thing is to have a manager who gives you a lot of confidence. Then you go on the pitch and give everything for the manager, the team and the fans. On the pitch, I never think what people are saying. All that matters is to try and look after the ball and do your best. At the time, that was what I was doing. I wanted to show my qualities. But, mentally, it was very tough.
"As a young player, to take all of this and the criticism, it wasn't easy at all. My life is good in Spain. Everything is going well for me. I am enjoying football and I would say La Liga is a league made for me. It is a very technical league and I am a technical player, so it suits me well."
Januzaj has three assists and two goals in 15 La Liga outings for Sociedad since arriving for around £9m.