Former Manchester United midfielder Nemanja Matic has blasted the Red Devils for making a ‘mistake’ during the summer transfer window. Manchester United completed five key signings throughout the summer transfer window which could well go down as one of the most successful summers since Sir Alex Ferguson retired from the club in 2013. Erik ten Hag’s United completed the signing of Paris Saint-Germain’s Manuel Ugarte with just hours remaining before the transfer window closed. It wasn’t just incomings at Old Trafford but also outgoings with Napoli completing the signing of Scott McTominay and J…