Not the worst. That could be a variety of players. This is the West Ham player that caused the most problems to his own team.
Answer: Mark Noble.
All season he never managed to get close enough to our centre halves when out of possession, leaving a massive gap for opposition to exploit and make a very average player in Diop look awful.
He lacked the ability to slide across and cover the full backs, something he was specifically asked to do by Moyes, when out of possession leaving some poor players double exposed.
He takes too many touches in possession and too much time (something Rice is copying from him) blunting the effectiveness of instinctive players like Antonio.
His lack of movement has lead to an overloading of central midfield all season (covering his deficiencies) meaning Rice has not been able to learn the position correctly. This is why when Rice plays for England, a more organised team, he looks double awful.
We bought Soucek to be Nobles legs and he is an awful, awful player. In effect Noble wasted our transfer budget for next season.
He has a real lack of discipline and self awareness. He doesn't play to his deficiencies and just sit in a 10 metre square and protect the defence. He let's his ego take over and feels the need to chase lost causes, get caught out of position and expose any other person in midfield.
Mark Noble, come and get your award.