At Adnan Januzaj's Manchester home, his most treasured football memorabilia stands proud.

Encased inside a frame adorning the living-room wall in the flat he still owns, Januzaj keeps the Manchester United shirt he wore on his full Premier League debut - the day he exploded on to the scene as an 18-year-old with two wonderful goals in a comeback victory at Sunderland.

Almost four years have now passed and sitting in a dimly lit room at Real Sociedad's Zubieta training ground this week, all that seems a long time ago.

Adnan Januzaj spoke exclusively to Sportsmail about his career in England and his future

The Real Sociedad winger was hailed as the heir to Ryan Giggs at Manchester United

The 22-year-old speaks to Sportsmail's Adam Crafton about his mixed career at Old Trafford

Januzaj is 22 now but in football terms, he is still to mature. To borrow the racing parlance of mentor Sir Alex Ferguson, he has not 'trained on'.

We should remember how fondly Januzaj was once regarded at Old Trafford. Ferguson gave him a place on the substitutes' bench for his final match in charge of the club at West Brom. David Moyes compared him to a young Wayne Rooney and Johan Cruyff. Ryan Giggs handpicked him to inherit the No 11 shirt he had worn with such distinction.

'Obviously that day was a dream,' Januzaj tells Sportsmail. 'To score two goals as a kid for the biggest club in England. As a 17-year-old, I trained a lot with the first team in Ferguson's final season. Amazing - Scholesy, Giggsy, Evra, Ferdinand... I remember Giggsy was always tackling me hard a lot. He wanted me to become a man on the pitch. He helped a lot during the difficult years I had with Louis van Gaal.'

After heading on tour during Moyes' first summer, Januzaj offered a rare bright spark in a tortuous campaign for the manager.

While more experienced colleagues retreated, Januzaj showed courage, exuding class and confidence. Everyone wanted a piece of him. A young woman tore into him in a tabloid newspaper because he took her on a cheap date to chain restaurant Nando's. He grins: 'Maybe I'd take her to McDonald's next time.'

Januzaj enjoyed a dream debut for United - scoring twice in a 2-1 win at Sunderland in 2013

The winger still has that match-worn shirt he wore on his full debut at his home - it is framed

Born in Brussels, Januzaj is the son of Kosovan-Albanian parents who escaped the Balkan crisis. His background meant he qualified to play for Belgium, Albania, Kosovo, Turkey or even England - should he have qualified under a five-year FIFA residency rule.

He had moved to United from Anderlecht as a 15-year-old without a word of English. His close friend Paul Pogba translated instructions in the early days of training at the academy.

In Albania, a TV show was broadcast entitled 'Hero or Traitor' and for a while the future of a teenager felt as though it would require a United Nations intervention to oversee a diplomatic conclusion.

England manager Roy Hodgson declared his interest. Januzaj was taken aback by the scrutiny. 'I'm born in Belgium, I grew up there. That's why I chose Belgium. It's where I'm born and it's my country. It was a great first year for me. After that year, it became harder.'

Januzaj's regression began when Van Gaal arrived in the summer of 2014. United pursued a galactico policy, recruiting Angel Di Maria and Radamel Falcao but Van Gaal's prosaic style of football shackled him further. Speed and penetration disappeared from United's play. Two years of the Dutchman brought yawns from the terraces and the schoolmasterly approach saw confidence slip away from Januzaj like water down a drain.

Roy Hodgson wanted to explore Januzaj playing for England before he chose Belgium

Januzaj enjoyed a great relationship with David Moyes before he was sacked as United boss

The same can't be said for Januzaj's relationship with Moyes' successor Louis van Gaal

'There was not the same freedom,' he says. 'A winger needs that confidence, a manager telling you, "Go and take people on". With him, it was a slow passing game.'

Januzaj sighs and rolls his eyes. Drawn-out and punishing group video analysis sessions did little to improve the mood. Did some players struggle with the brutality?

'For some it was difficult. You could see some players were not enjoying the football. The manager and I had many difficult meetings.

'I was frustrated and everyone could see that I was not the same Adnan as the first year. I was sometimes even in the stands. When you work hard in training and then get left out, it's hard for a young guy.'

Van Gaal's philosophy restricted United. 'It was not only me. As a footballer, if you think too much on the pitch, it is never good. You need instinct in your play. When the ball came to us, we had to stop and think, "What are we going to do with it here?", "I can't lose the ball".'

Under Van Gaal, Januzaj felt restricted as a footballer due to his robotic philosophy of football

'Everyone could see that I was not the same Adnan,' Januzaj said about his time under Van Gaal

Did it reach the stage he feared losing his place if he chose flair over Van Gaal's robotic instructions?

'Yes. That kind of stuff comes into your head. It was difficult... training sessions too. Under Ferguson, it was always intense. People wanted to win in training. It started to change.

'It was not the United we used to see winning games and winning trophies. Teams used to come to Old Trafford and be scared to play. I had the sense that some teams started coming to Old Trafford thinking,"We can beat them today easy".

Januzaj started eight games in Van Gaal's first season and was then loaned to Borussia Dortmund. He did not start a league game in Germany before returning in January. Manager Thomas Tuchel claimed he did not possess the necessary 'motivation or attitude'. A narrative developed that Januzaj's determination had lessened as he enjoyed the perks of a lucrative five-year contract.

His loan at Borussia Dortmund was short-lived after falling out with then-boss Thomas Tuchel

Januzaj lavished praise on former Manchester United winger Ryan Giggs, who coached him

He bristles. 'If I only played for a contract, I would have stopped football right away. Since I was a little boy, I have loved this game. I started from age four and it's all I wanted.

'Those suggestions are stupid. I had very good stats when I came on. Sir Alex texted me and called during that spell. He told me, "Keep working hard, never give up, life goes on, you have quality and never stop working". I needed that.

'Giggsy was assistant during Van Gaal's time. He always talked to me and tried to help. He could see I was not the Adnan everyone knows.'

When Jose Mourinho arrived, a loan move to Sunderland and a reunion with Moyes followed. It was a hellish campaign in which Januzaj was booed by the club's own support on the way to relegation.

Jose Mourinho (right) let Januzaj go out on loan at Sunderland before selling him to Sociedad

His time at Sunderland (left) was sometimes hellish but he's looking to rebuild a career in Spain

'People were criticising me as though I was the only player playing for Sunderland. I am a young player, still learning. I always gave my best. I was always the one trying to make something happen. Sunderland have never been in the top four so you know it will be difficult.'

This summer, Mourinho allowed Januzaj to leave in a permanent deal to Sociedad. Belgium coach Roberto Martinez is an admirer and privately put in a word earlier this summer with the Basque club.

'Jose had to make things happen very quickly and make quick decisions,' Januzaj says. 'I had not been playing for two years. He is a great manager and he has been fair to me because he let me leave to improve somewhere else. That's how the world goes and I look forward.

'I know Sir Alex is always at the end of the phone. The same with Giggsy and David. Those people will always back me. My first job now is to impress here. I'm hoping for a World Cup place. The world does not stop.'