The player's cleats make contact with the opponent's chest. Depending upon the speed & angle, a ref has a very easy call there. Especially if embellished by the struck player.
It is a stupid & reckless play by Nani. There is little to be gained by that raised foot there. It occurs towards midfield, not on the end line or sideline in an attempt to rescue a wayward ball. Did the player not think there was anyone else behind the play? I have no idea why the defender doesn't just get in proper position to defend the attacker & cede possession there. United looked pinned in; I don't suspect he's toe poking the start of a 60 yd break.
A very unusual choice by a defender there, and a stupid play with nothing to be gained...but as it turned out, everything to be lost.