I reckon there is working hard and there is working hard. Mario has been tracking back closing down, participating in our pressure game. The traditional English version of trying hard.
Compare that to a player like Tevez Suarez or Costa. They don't track back all the time, what they do is always make the runs, always make the space, never give the opponent a second of peace whether they have the ball or not. Mario still lacks that energy when we're moving the ball around and thats an area he needs to improve.