Depends who you are playing on the left, I would suggest looking to promote the youth that is already there, perhaps training Niang as an AMR if he not accomplished already? (cant quite remember what AM he plays might be AMC) anyways back to the point, niang will develop well especially with those around him. Or if you really do want to bring in a winger I would suggest looking at Lamela (he is left wing but i'm pretty sure can play right also), try and see if you can get Agustin Allione plays winger but for me was amazing. Another player you might try is Kevin Mirallas, not sure what his stats are like on LFCs update but he did well first season at Everton in my United save. Also look at Alexis Sanchez he often becomes transfer listed and can be a good buy.