Marcus Rashford is Manchester United's eighth youngest Premier League player. He was 18 years 119 days when he made his league debut against Arsenal on 28 February

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To chart Marcus Rashford's astonishing rise from obscurity to first-choice striker in an FA Cup final and a place in Roy Hodgson's provisional England squad for Euro 2016, you must begin with a fifth-round tie at Shrewsbury on 22 February.

Rashford, 18, was not involved in Manchester United's 3-0 win. He had made a rare start for the Under-21 team at Manchester City two days earlier.

But what happened at the Greenhous Meadow was to have enormous consequences for Rashford, United and, possibly, England.

Will Keane was the unlucky man, forced off 11 minutes from the end, nine minutes after being introduced as substitute.

Without Keane's groin injury, Rashford probably wouldn't even have been on the bench the following Thursday for the Europa League tie with FC Midtjylland.

In that case, there could have been no last-minute call-up after Anthony Martial got injured in the warm-up - so close to kick-off manager Louis van Gaal was left one substitute short for the match - and there would not have been the two debut goals that launched Rashford on an amazing journey that could yet end with a place at Euro 2016.

The best at eight

Rashford was a product of the Fletcher Moss Rangers junior club in Manchester

Of course, Rashford's rise did not really begin as recently as February.

He comes from Wythenshawe, in south Manchester, and was encouraged to join the local Fletcher Moss Rangers external-link boys club by his dad, Robert, who was a coach there.

Pretty quickly, Rashford came to the attention of Manchester United.

"He was eight when he went to the development centre, and came into the academy at nine," said Paul McGuinness, who was a coach within United's academy for 24 years until his departure in February.

"The talent was obvious. There are late developers but quite often, if you are going to be the best, you are the best at eight. Danny Welbeck and Jonny Evans were top in their group right the way through. Ryan Giggs would have been the same.

"It was Marcus' movement that set him apart. His running was very smooth and elegant.

"But it wasn't just his ability. He was self-driven and curious. He always had a trick, and practised any chance he got. Even when he was picked up to go training, the coaches would frequently find him knocking a ball on to the roof of a shed or a garage and trying to control it as it came down. Either that or he would be chipping a ball into a bin."

The sulky phase

Marcus Rashford (bottom left) has swiftly become a fans' favourite at Manchester United with his goals

To an outsider, Rashford has emerged from nowhere to become a Premier League star.

It is true that he only made his first-team debut on 25 February, and that by the time he played Bournemouth on Tuesday, a day after he was picked in England's provisional 26-man Euro 2016 squad, he was scoring his eighth goal in 17 appearances.

But the work that goes into making a Premier League footballer is immense. And it is not always straightforward.

"The term 'emerged from nowhere' is an interesting one," said McGuinness.

"Marcus has already been on a long journey from where he started off. He had a little period, around 14 and 15, when he struggled because he grew quickly. It happens to a lot of players during growth and development. His legs were growing very long and he lost co-ordination.

"While it was happening he was frustrated because he couldn't do the things he normally would. He was a little bit sulky and a little bit moody because of it.

"Then there is the sheer physical effort required to take the step up to each level.

"One of Marcus' first games for the Under-18s was at Newcastle. He was on the wing and he was running and running. Even in the first half, his body language was screaming 'Oh god, I didn't realise I had to do this much'. It was crying out for him to come off. We kept him on.

"He was 16 in an underdeveloped body playing under-18 football. You have no idea how much the extra intensity takes out of you."

Learning to be a striker

Marcus Rashford's emergence has been one of the main plus points in Louis van Gaal's second season as Manchester United manager

Once he had made the switch to United's Under-18 team, he was under McGuinness' direct control.

At 50, McGuinness has spent the majority of his life at the club, first as a player, then a coach.

It was his team, containing Paul Pogba and Jesse Lingard, that won the FA Youth Cup in 2011. McGuinness' experience is vast.

Together with his coaching colleagues, he sensed more could be made of Rashford's talent.

"He wasn't goal obsessed," he said. "He would play up front but he was always wanting to be the clever number 10.

"Someone with that much ability and speed is wasted doing that.

"It happened with Cristiano Ronaldo. When he first came he was all tricks and stepovers and show. Then he started to realise that goals got you all the attention. And he changed didn't he? He started to score headers. He saw what could happen if he changed to a striker's mentality."

So the work on Rashford began. His body shape, his runs, his timing. How he received the ball. Practice, practice and more practice.

"We won a good indoor tournament in Germany in front of 6,000 people," said McGuinness.

"We used it specifically with Marcus to work on receiving the ball one on one with his back to goal."

The pivotal decision

As recently as December, Rashford was playing for United in the Uefa Youth League

Rashford had always been ahead of his age. Really, he should have been elevated into Warren Joyce's Under-21 squad on a permanent basis this season.

But a summer conversation between McGuinness and Joyce has had a dramatic outcome.

Former Crewe Alex striker and prolific non-league goalscorer Colin Little was given the job of showing Rashford how to be a centre forward.

"He needed to work specifically with Colin on his finishing, his movement, receiving the ball chest forward rather than with his back to goal," said McGuinness. "He would learn how to get on the shoulder of the last man, quickly swing his hips round and run sideways to open up the space for a pass. Lots of little details.

"We did that lots and lots. We directed a lot of team practice on it. We targeted him because he deserved it. We thought he could be a first-team player.

"He has missed the Under-21s now. But he still needs the work. He is not the finished article."

It's up to him now

Marcus Rashford with his grandad Ces

McGuinness will be watching Rashford's development with a more detached perspective from now on.

Since leaving United he has kept himself busy visiting a number of clubs to offer advice on youth coaching. He also had a brief stint with the England Under-18s. He hopes to use his experience as a head of coaching, or academy manager, or even as a first-team manager at a club committed to youth development, although he accepts "you cannot always choose".

For now though, McGuinness is enjoying Rashford's ascent.

"It will be great to see him play in the FA Cup final," he said. "Marcus is a great lad and very humble. When I left United he was the first to send a text to say thanks for the work we had done.

"He is not there yet. He still drifts about, and he'll need a bit of luck in avoiding injury.

"But he has given himself a good foundation. It is up to him to build on that. Nobody else can do it."

Marcus Rashford's world has been turned upside down since his first appearance of the season, in a 1-1 draw at West Brom's training ground in an Under-18 game on 8 August

The Mersey Bank playing fields in south Manchester where Marcus Rashford learned how to play

Marcus Rashford is a pupil at Ashton-on-Mersey School

Marcus Rashford (left) in action at the 2015 Mercedes-Benz Junior Cup

Marcus Rashford was chosen as Manchester United's Under-18 player of the year for 2015-16 by the club's Head of Academy, Nicky Butt (left)

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