Diogo Dalot isn’t a name that many Manchester United fans will have been overly familiar with prior to this summer.The 19-year-old only made a handful of league appearances for FC Porto last season but did feature against Liverpool at Anfield in the Champions League.His performances caught the eye of United’s Portuguese head coach Jose Mourinho, who convinced his employers to fork out a reported £19 million for the youngster’s services last week.Dalot, who is capable of playing at both right and left-back, will provide competition for the likes of Antonio Valencia and Ashely Young next season.Mourinho has already claimed the teenager possesses the talent to become “a great player” for the Red Devils and believes there’s no better young full-back in world football at present. High praise indeed.“Diogo is an extremely talented young defender with all the qualities to quickly become a great player for this club. He has all the attributes that a full-back needs: physicality, tactical intelligence and technical quality, combined with a Porto Academy mentality which prepares players for the maturity they need at the professional level,” Mourinho told United’s official website.“In his age group, he is the best full-back in Europe and we all believe he has a bright future ahead of him at Manchester United.”

United fans are concerned by latest photos of Dalot

“Joining Manchester United is an unbelievable opportunity for me,” Dalot added. “I have grown up in Porto's Academy and I am so thankful for everything they have done for me. But the chance of coming to the biggest club in the world is something I just couldn't turn down.

“I'm excited about working with Jose Mourinho and learning everything I can from such a successful coach. I am looking forward to playing alongside the fantastic players in the squad.”

However, United fans are now feeling a mixture of confusion and concern after photos emerged showing Dalot on crutches, just days after passing his medical.

The defender was spotted hobbling around Manchester, leaving fans wondering what on earth was going on.

The reason why Dalot is on crutches

The Sun, however, have discovered the reason why Dalot is currently on crutches.

It turns out that United have signed the full-back knowing that he has a slight injury to his knee.

Keen to ensure he keeps the weight off the knee, the medical team at Carrington have instructed him to use crutches.

The Portuguese starlet has been told by United to rest, while a source has told SunSport that they "hope he will be ready for start of pre-season but are refusing to rush him".

As things stand, Dalot is still expected to be part of United’s squad for the pre-season trip to America, where he will continue his conditioning work.