#4 Ashley Young
Ashley Young was actually so poor in this match that fans called for him to retire after the game. He was booed off with the rest of the United squad for their dreadful performance and it was made clear that things need to change for Red Devils, before they face even more losses.
Young didn't win a single aerial battle and cost United the first goal when he stumbled in front of Messi, who snatched the ball and went on to score the opener.
He began to recover his form somewhat later on into the match, but by that point, the damage had already been done. Young couldn't handle Lionel Messi down the left flank and when he was responsible for marking Suarez, he lost him consistently as well.
It didn't help matters that the rest of United's defence were poor, too, but Young was rightly singled out as one of the worst players out on the pitch that night, and I don't think anybody can dispute that.