Jadon Sancho completed his loan return to Borussia Dortmund this week (Getty)

Kieron Dyer believes Jadon Sancho displayed a ‘red flag’ long before his bust-up with Erik ten Hag at Manchester United.

Sancho was frozen out of the United first team in September following a dispute with Ten Hag over his effort levels in training.

United’s £73 million signing from Borussia Dortmund was ordered to train away from the first-team squad once it became clear that his standoff with Ten Hag would not be resolved quickly.

Reports have since surfaced that United had issues with Sancho over his lateness and Dyer, who made over 220 Premier League appearances during his playing career, believes the United winger showed signs of ‘quitting on his own teammates’ when he failed to get the better of Reece James during Manchester City’s defeat to Chelsea in the FA Youth Cup final in 2017.

‘He [Sancho] was a wonderkid growing up. He was the talk of everybody in the academies at that time,’ Dyer told talkSPORT.

‘I was coaching and when I watched Man City he was unstoppable. It was the youth team, so the under-18s and he was incredible.

Kieron Dyer claims Jadon Sancho showed questionable mentality after failing to get the better of Reece James during the FA Youth Cup final in 2017 (Getty)

‘He was probably 17 years old and everyone wanted him, he could have his pick, he’d just dominate every team.

‘They played Chelsea in the FA Youth Cup final and played against Reece James and Reece James got the better of him, which can happen to anyone, but he quit on his team in the Youth Cup final.

‘He just mentally went and I kind of had a red flag against him then and thought that’s a bit weird.

‘He’s got the world at his feet and alright, he’s had a bad game but he’s quit on his teammates.

‘You could see the life had gone out of him, he’d stopped tracking back and sort of given up and was basically mentally gone.’

More: Trending

Dyer, however, has backed Sancho’s decision to join Borussia Dortmund as he may find Ten Hag has been replaced by the time he returns to United in the summer.

‘You’ve seen the problems since at Manchester United and I sort of sensed that as a 17 or 18-year-old kid and it’s sad because he’s got some talent and some ability,’ Dyer said.

‘I think it’s a good move because if he does do well in Germany then there’s a good chance that when he comes back to Manchester there’s going to be a new manager, which could definitely happen the way that Erik ten Hag and Man United are going.

‘It could work out well for him.’

For more stories like this, check our sport page.

Follow Metro Sport for the latest news on Facebook, Twitter and Instagram.

‘I kind of had a red flag against him.’