Former Manchester United defender John O’Shea has picked one player he thinks could be the key man against Liverpool on Sunday. This weekend sees Manchester United take on Liverpool in what is a must-win FA Cup game. Given how the season so far has gone, the FA Cup is probably the only chance United have to salvage something from this campaign. Erik ten Hag is expected to rely on the youth in this game as he has for much of this campaign as Alejandro Garnacho, Rasmus Hojlund and Kobbie Mainoo have all emerged as pivotal players. Now one of these three has been tipped to play a main role this w…