Januzaj's career trajectory has significantly flattened out after its initial heady rise. His emergence was one of the very few bright spots of David Moyes' time in charge of the Red Devils in 2013/14, and there was for a time tremendous excitement about his potential.
All of that potential is presumably still there, but in order to restore a trajectory of ascent, he will need to make some changes and a few breaks to fall his way.
Let's take a look at three ways he can revive his career at United, to live up to the hype he understandably generated with his impressive start.
Improve His Attitude
Of course, being on the outside looking in, there is only so much you can know about a player's attitude. When Moyes was in charge, he was full of praise for his charge's approach to the kind of heavy on-pitch attention Januzaj received from defenders. Back in October 2013 Moyes said, per Sky Sports:
If ever there was a boy who can take it, it will be him. You just hope the referees give him the correct protection, and I'm sure they will, but he won't be moaning about it.
He's a great lad and he'll bounce up and get on with it. You can kick him as hard as you like and it won't affect him.
However, fast forward to February 2015, and Louis van Gaal's comments on Januzaj, per the Express, had a much less flattering tone. Van Gaal said of Januzaj's relative lack of involvement in the first team:
I observe players every day of every week and communicate what I want from them. And they have to show it. If I think 'Okay, he is now ready to play' then maybe I let them play.
Januzaj has a lot of talent but you have to perform that talent in the matches and also in the training sessions. I do not make the line-up, the players themselves make the line-up.
The competition is high in this squad and I have to compare players. It's not just Januzaj, I have said the same to [Radamel] Falcao and [Juan] Mata.
It's difficult for me to manage but also difficult for the player himself to manage. Is Januzaj managing it well? You have to ask him, it's not for me.
The subtext of that statement—and Van Gaal's subsequent decision to send Januzaj out on loan—would seem to suggest the player has not convinced the manager.
And speaking of that loan, it was hardly a successful demonstration of motivation. During that time, Januzaj "turned down an opportunity to link up with" the Belgium under-21 squad," per Sky Sports.
That squad's manager, Enzo Scifo, told Belgian newspaper La Derniere Heure (h/t Sky Sports), "A 20-year-old player who gives this impression of non-motivation, it reflects a poor state of mind."
In the same paper (h/t Sky Sports again), Januzaj's agent, Dirk De Vriese, refuted that claim, saying:
There is no question of a bad state of mind, Adnan focuses on his work and we plan the rest. Do not point the finger.
[Borussia Dortmund] are doing well and is a real machine. The current Dortmund is one of the best teams in Europe.
Remember that Adnan did not have pre-season with them. Dortmund have given him time to adapt and we must do the same.
That rebuttal rings particularly hollow in hindsight. At the end of his time with Dortmund, manager Thomas Tuchel's remarks about Januzaj painted an unimpressive picture.
Tuchel told Bild (h/t the Independent), "It is a pity he did not show the desire and attitude you need to progress at his age."
This would certainly appear to be something Januzaj will have to work on if he wants to succeed at United.
Wait Out Van Gaal
This one is a little speculative, but honestly, perhaps the best thing for Januzaj would be for Van Gaal's time in charge to come to an end.
Van Gaal's quote above hardly demonstrated he saw the youngster in a good light. That seemed to have changed when Januzaj was put into the side at No. 10 against Aston Villa and Newcastle United in the second and third games of this season respectively. He was pretty impressive against Villa, combining with Mata for the game's only goal.
Then, in a surprise move, the end of the transfer window saw him loaned to Dortmund.
At that point it was pretty clear the manager—whose attack has consistently shown a lack of the kind of creativity and spark Januzaj at his best can certainly provide—did not see the Belgium international as the answer.
Waiting out Van Gaal and hoping the next manager holds him in higher esteem could be Januzaj's best tactic.
Of course, this one is not in Januzaj's control, but even if his attitude has been a problem in the past and he knuckles down, he will need fortune to smile upon him to change his standing.
He needs players in the positions he can fight for—all three of the spots behind the striker and maybe on occasion even the centre-forward role—to be unavailable or out of form, and he needs to hit the ground running when he gets his chance.
He needs Van Gaal to be flexible enough to change his mind on him or he needs Van Gaal prospective replacement to believe in him.
Sadly, a player who looked to have a great United career laid out for him has stumbled in his development. He will need plenty of good fortune—in addition to a lot of hard work—to revive his Manchester United career.