Arsenal are set to challenge Manchester City and Liverpool for the signature of one Premier League left-back this summer. Arsenal and their two Premier League title rivals, Liverpool and Manchester City, are all keeping tabs on one top flight full-back. It is vital that Arsenal invest in a new left-back in the upcoming summer transfer window. It has to be a top priority for Mikel Arteta. The Gunners’ current options in that part of the pitch all leave something to be desired. Discounting Jurrien Timber, who has spent practically the entire season sidelined by injury, Oleksandr Zinchenko, Jakub…