its more of a problem, if he has a very weak left foot and is used to get taken on by players from the right he may feel uncomfortable getting attacked on the side where his left foot is.
most of the time attackers or wingers in that case try to get be the outside of the player so every winger would play against his weak foot.
passing wise its difficult too, because when he is at the byline on the left and wants to pass inwards he either has to twist his ankle to pay a side-footed pass or use the his week foot ...