Even ignoring the headbutt, he was in trouble with Atkinson. Watch the replay of the entire sequence. Atkinson is waving him to come with him after the second tackle, before Aguero provokes him.
It was just such a stupid piece of play. He could easily make the first foul without getting himself a yellow card. Instead he left the ref no choice.
He could also easily not waste time debating a clear cut yellow card with Atkinson, so he wasn't behind the play having to chase back against Aguero, who obviously angled for the second foul.
He then could easily just not make the second foul, as Aguero was going into no mans land and we had the situation well covered.
And then, to top it off, he got goaded into a headbutt, leaving us on our barest bones in midfield for the upcoming matches as well as killing every minimal chance of getting a win in the match.
I've been defending him this season and think he's done well enough to be a squad option for us. But surely, surely, his only saving grace was that he's supposed to be a reliable option in midfield, doing the basic things unspectacularly but well?
He's now cost us stupid penalties vs Everton and Watford, and he's getting himself sent off in just about the stupidest way I've ever seen, during our most important part of the season, with injuries all over the place.
Now I can live with him slowing play down, being a poor passer of the ball and generally not being of the quality a Manchester United midfielder should be. It's not his fault, and deployed correctly he can sort of do a job.
But yesterday was his fault, and I'm afraid, judging by Mourinho's reaction, that it might very well have cost him his underwhelming United career.