Arsenal could now be set to go toe-to-toe with Manchester United over the signature of one mutual transfer target. Both Arsenal and Manchester United are keen to bolster their defensive contingents in the summer transfer window. Mikel Arteta has already constructed a remarkably effective defensive unit at the Emirates Stadium. However, it lacks strength in depth. William Saliba made Arsenal history last season as he became the first outfield player to ever play every minute of a Premier League campaign for the club. His centre-back partner, Gabriel Magalhaes, also played an awful lot of footba…