Wayne Rooney has been warned about his improper conduct by the Football Association after appearing to mouth "12 men" into a television camera following United's defeat at Chelsea.
The United striker made the comment as he left the pitch at Stamford Bridge, an obvious reference to the performance of the referee, Martin Atkinson.
An FA spokesman said: "Wayne Rooney has been warned as to his future conduct following remarks made yesterday."
His manager Sir Alex Ferguson will not face any action following his criticism of Atkinson. Ferguson condemned the decision to award the free-kick that led to Chelsea's winning goal as "absolutely ridiculous" and said such decisions mean people "lose faith in refereeing".