England's Luke Shaw admitted watching the World Cup from afar provided the motivation he needed to grow up and start delivering on his potential for Manchester United.

Shaw was the world's most expensive teenager when he signed for United from Southampton for a reported £27 million in 2014, weeks after representing England at the World Cup in Brazil.

However, after four years overshadowed by criticism over his diet, a horrific leg break in 2015, and being routinely dropped by United boss Jose Mourinho, Shaw has been one of few bright sparks in a difficult start to the season for Mourinho's men.

Shaw was just another fan as Gareth Southgate's England side captivated the hearts of a nation in reaching the semi-finals of the World Cup in Russia.

But he wants to be part of the feel-good factor around the England team after earning a recall to Southgate's squad for Saturday's Nations League opener against Spain to kick-off qualification for Euro 2020.

"That made me want it more. The World Cup is the biggest stage for any footballer. It was wonderful to see how well we did as a team, and how far we got was brilliant. But also it was quite gutting not to be there," said Shaw on Tuesday.

As a result, he went away to do extra training in Dubai over the summer to get fit for the new campaign and impressed Mourinho in an otherwise troubled pre-season tour of the United States.

"I've matured, grown up. I've gone from a kid to a man now, and I know what I need to do to push myself. I want to play for Manchester United, to stay there and fight for my place, and prove my worth to the team," added Shaw.

"I want to do the same here now and give Gareth a headache over selection."

Mourinho has at times been stinging in his criticism of Shaw, but the former Southampton full-back insists the Portuguese coach was just trying to get the best out of him.

"Mentally it made me come out the other side and made me stronger, to want to prove to him that I can do what sometimes, in the last couple of seasons, he'd said I couldn't," added Shaw.

"I think, at times, he got frustrated with me because he knew I could do better. Maybe when I look back at times, maybe he was right.

"I had a chat with the manager before the season and he said he wanted me to stay and fight for my place, and that motivated me a lot in the off-season. I came back and played games in pre-season, and now I have my fitness fully and everything is good.

"If he didn't trust me, it would have been easy for him to say he wanted to sell me. But he always believed in me."