It looks like Costa is mentally spent, and perhaps he isn't the world class striker many have made him out to be. Earlier in the season I thought he would've been a good addition to the United squad, providing a rotation option as well as a long term successor for Zlatan. However, he has been abysmal since the turn of the year. His finishing has been poor, and his passing has been wayward. I'm surprised that he hasn't been dropped yet. What exactly does he offer? He fouls players all the time, he dives, and is more of a liability than an asset to his team mates.
That goal he "scored" was extremely fortunate and will probably be chalked off as an own goal.