Per The Guardian:
Sergio Agüero will face no action for his apparent stamp on the West Ham captain Mark Noble in Saturday's loss at Upton Park and is free to play in Sunday's derby against Manchester United.
The City striker, who has scored five goals against United in his past six games against them, left Noble in pain during City's 2-1 defeat but will avoid retrospective punishment from the FA because the incident was seen by the referee, Martin Atkinson.
I have to admit this one was missed on Saturday during the game and it was only later when I got a couple of messages about it that you realised Aguero was more than a touch fortunate.
What has saved him from retrospective action is the fact Atkinson saw it, and presumably you think - at the time anyway - he may have thought it was simply a mistimed challenge, with no real malice. Atkinson was certainly well positioned at the time but you have to think that if he had not seen the incident at the time Aguero may now be looking at the prospect of a three game ban.
As it is, Aguero is free to play both against Newcastle this Wednesday and, of course, the derby this weekend.