Luke Shaw thought he had done OK as he walked off the Old Trafford pitch at half-time during Manchester United’s FA Cup tie against Arsenal last month. Steady, nothing special, but he felt invigorated all the same. The score was 1-1 and Shaw, returning to the team for the first time since United’s defeat at Swansea City in February, had kept Arsenal flyer Alex Oxlade-Chamberlain reasonably quiet. Shaw was growing into that famous red shirt, getting stronger down the left flank as this fiery sixth-round tie against Arsene Wenger’s team wore on. Luke Shaw thought he had done OK against Arsenal in the FA Cup but he was substituted at half time . Louis van Gaal substituted the £28million defender, telling Shaw that he was not fit enough to play for United . Shaw has not played since and was withdrawn from the recent England squad as he struggles at United . Shaw's stats for the season show how he has struggled to hold down a regular place at left back with United . What happened next will ultimately shape his career as a United player. Louis van Gaal substituted the £28million defender, telling Shaw that he was not fit enough to play for United, and replaced him with Phil Jones for the second half. Arsenal went on to win 2-1 and getting dragged off at half-time was another blow to Shaw’s fragile self-esteem. He has not played since, withdrawn by Van Gaal from the England squad for games against Lithuania and Italy because of question marks over his fitness. His position at United has been taken by Daley Blind, shuffled across from the centre of midfield as United went on a winning run against Tottenham, Aston Villa, Liverpool and Manchester City. Shaw is struggling to come to terms with his new life, turning to United’s psychologist to declutter his mind and reboot just nine months into his career at Old Trafford. Shaw is struggling to come to terms with his new life and has turned to United's psychologist of late . Shaw had kept  Alex Oxlade-Chamberlain reasonably quiet in the FA Cup clash but Van Gaal was unimpressed . There are serious concerns, particularly because his parents have spoken to the club about a lack of structure and support for their teenage son. They have every right to do so. Cash is king in football and we sometimes forget to look beyond the £28m fee United paid Southampton (£15m up front) and a five-year contract worth an eye-watering £90,000 a week. Shaw was 19 in July, returning from England’s disastrous World Cup in Brazil, where he started the final group game against Costa Rica, to meet up with his new United team-mates. Initially he lived in the Lowry Hotel, joined by his parents as he began a period of adaptation in a new city. He has since moved into a house in the suburbs. Earlier this week he hinted at some of the difficulties he has faced, awarding himself a C minus for his first season during an interview with Match of the Day magazine. At United, Shaw has found a manager in Van Gaal who has very specific and exacting demands of his players . Van Gaal has led United up the table and they crowned the recent good form with a win over Manchester City . He was assigned a dietitian and given nutritional advice as he adjusted to life as the most expensive teenage footballer in the history of the game. At Southampton he had been ordered to eschew the glasses of cola and sticky food, told to mature into his physique as he grew into a man’s body. He needs discipline and constant, caring reminders from the coaches. Those close to him explain that Shaw needs pastoral advice, that he responds positively when he feels close to the coaches and playing staff. At the age of 16, when Chelsea made an official offer for Shaw in his breakthrough season at Saints, his head was so scrambled by the prospect of joining his boyhood team that he had to be taken out of the Southampton line-up. In the dog-eat-dog world of United, where it is a constant fight for survival after last season’s disappointing finish, he has yet to establish those strong bonds. Last season he often spent time in Mauricio Pochettino’s office after training, sitting with the former Southampton manager as they discussed different areas of their lives. Mauricio Pochettino spent a lot of time with Shaw to help make him feel at home at Southampton last season . Pochettino teased the best out of a player who went on to make his England debut at the age of 18 . The club worked out that he was travelling back to his parents’ home near Cobham, Surrey, by monitoring his Twitter account and looking at the times he posted messages on social media. With Pochettino there was a real, almost paternal warmth to their relationship as the manager teased the best out of a player who went on to make his England debut at the age of 18. To put Shaw’s extraordinary rise into perspective, Kenny Sansom, perhaps England’s classiest and finest left back, had to wait until he was 20 to make his debut for the national team. Shaw’s life has changed, moving away from the bosom of his family in Surrey for the demands and challenges at a club where the spotlight is intense. He is a sensitive young man. It had been hoped that Van Gaal would show some patience with Shaw when his appointment at United was confirmed, particularly after his Champions League success at Ajax in 1995. Marc Overmars (22), Michael Reiziger (22) and Clarence Seedorf (19) all started the 1-0 victory over Milan in the final in Vienna, with striker Patrick Kluivert (18) named on the bench. Van Gaal's Champions League success at Ajax in 1995 saw him include young players in his starting XI . At the 2014 World Cup with Holland, Van Gaal had notable success with 20-year-old Memphis Depay . More recently, at the 2014 World Cup with Holland, Van Gaal had notable success with 20-year-old Memphis Depay, who was named on the three-man shortlist for the best young player at the tournament. But what Shaw found at United was a manager who has very specific and exacting demands. Before Van Gaal conceded defeat and reverted to a back four, Shaw had been playing in the unfamiliar role of wing back. The transition has many similar characteristics to Gareth Bale’s first couple of seasons with Spurs. Both are real home boys. Shaw's position at United has been taken by Daley Blind, shuffled across from the centre of midfield . The former Southampton man is learning to deal with the attention at one of the biggest football clubs around . Shaw longs for the days when he could stay behind after training with Pochettino, where the Argentinian coach would team up with one of the other young players for a light-hearted game of head tennis. It was at Southampton, under the guidance of Pochettino and the former executive chairman Nicola Cortese, where Shaw’s career flourished. The well-being of the boy was top priority. He is a United player now, learning to deal with the attention at one of the biggest football clubs in the world. At such a young age, he needs all the help he can get.
Manchester United paid almost £30million to sign Luke Shaw last summer .
Deal made Shaw the most expensive teenage footballer of all time .
He has not appeared for United since being substituted against Arsenal .
Louis van Gaal has told the young left back he is not fit enough .
Shaw is a home boy and has struggled to adapt to new life in Manchester .
He has found  a manager who has very specific and exacting demands .