Patrice Evra's form has been hit and miss since 2010, with United routinely looking for future replacements.
Sir Alex Ferguson signed Alexander Buttner in the summer of 2012 but it is clear that, whilst he is an adequate understudy, he won't ever have the quality to start week in week out for United.
Ferguson was reportedly a fan of Leighton Baines but David Moyes, the Everton manager at the time, refused to sell him. When Moyes took over at United, he also attempted to lure the left-back to Manchester but had no luck. Baines has since signed a new contract with the Merseyside club and is very unlikely to make the move now. With him turning 30 later this year, United are unlikely to want to fork out a large fee for him now too.
United do need a new left-back though and there are several requirements. Not only do they need to be able to defend well, but a full-back at United spends more time going forward and crossing the ball in to the box than they do defending. So who are the players they should be trying to sign this summer?