http://www.guardian.co.uk/sport/blog/2010/mar/24/the-question-inside-out-wingers

Wide forwards can be stopped, but it takes a major change for the defending team. Alvaro Arbeloa's marking job on Messi for Liverpool in 2007 shows how effective it can be switching a right-footed full-back to play on the left flank, and Young's slightly stuttering form for Aston Villa earlier this season shows what can happen when full-backs get used to showing a player outside rather than inside.
But then a player of the class of Ronaldo or Messi (as he is today) will simply go outside (could that, in fact, be why Barça bought Zlatan Ibrahimovic, to give them an aerial presence if Messi were forced into crossing more often?), and playing a right-footer at left-back or a left-footer at right-back immediately impairs their capacity to overlap.