​Manchester United fans would be forgiven for wondering where Kobbie Mainoo was when the club released a batch of images from the first day of pre-season training last week. After all, he has not played a minute at the World Cup, so where could he be?The answer, unfortunately, is that he has spent the last six weeks warming England’s substitute bench. This, for a player of Mainoo’s calibre, is simply unacceptable and yet another blow in what has been a tricky season for the academy graduate.AdvertisementAdvertisementAdvertisementWhile hopes are high that football might finally be coming home, Mainoo has likely given up all hope of playing a single minute in this summer’s tournament and will probably be counting the days until he can return to United and Michael Carrick, a manager who truly respects him.Since Carrick took charge at the Red Devils in January, Mainoo has reminded everybody of the immense skills he possesses. These are skills that were, for some unknown reason, completely ignored by former United manager Ruben Amorim.Despite having played barely any football in the first half of the season, the England international excelled after returning to the game and played a pivotal role in United qualifying for the Champions League. His incredible performances, which peaked in a goalscoring display against local rivals Liverpool, rightly attracted the attention of England manager Thomas Tuchel, who opted to include him in his World Cup squad.AdvertisementAdvertisementAdvertisementIn the build-up to the tournament, Tuchel insisted that every England player knew their role within the squad. However, this seems incredibly unlikely in the case of Mainoo.Having played a key role in the last Euros, even starting alongside Declan Rice in the final, the United academy graduate would have expected to provide stern competition for former United target Elliot Anderson.Things have not played out that way and, as bizarre as it is, Mainoo now seemingly finds himself behind Eberechi Eze and Reece James in the central midfield pecking order. When Rice was substituted against Norway last weekend, the manager looked past his only fit central midfielder on the bench and instead sent on a right back to fill the void.AdvertisementAdvertisementAdvertisementIt is a testament to the temperament and patience of Mainoo that he has not kicked up a fuss or shown any disrespect towards his international manager, but the talented youngster must be wondering what could have been had he remained with United for pre-season.Had Mainoo not made the England squad, he would have been able to enjoy a period of extended rest before reporting back to pre-season with his club and teammates. Furthermore, he would have been able to build up a relationship and understanding with his new central midfield partners.As it stands, Mainoo will likely have no chance to properly train with the likes of Andrey Santos and the Manchester United-bound Youri Tielemans before the Premier League