The FA have written to Chelsea coach Avram Grant to ask him to explain his remarks about referee Steve Bennett.
Grant called Bennett's integrity into question after Manchester United's 2-0 win at Wigan last Sunday earned a 10th Premier League title for Sir Alex Ferguson.
Chelsea, level on points with United before kick-off, could only draw at home with Bolton.
But Bennett came under fire for not awarding the home side a penalty for handball and then opting not to send off Paul Scholes for a second bookable offence when he fouled Wilson Palacios.
At his Champions League media conference on Wednesday Grant said: 'I told you that I believed in the tradition of the fair English game. I will not say anything against it. But what happened is what I expected.
'In England there are very good referees, but there are some - a few that you can influence, like you saw.
'I think in our game against Manchester United at Old Trafford, the referee (Mike Dean) influenced the result for sure. We know that.
'I think the red card for Mikel John Obi in that game should not have been a red card, I think that Paul Scholes should have had a red card on Sunday and Wigan a penalty also. But it is finished. I congratulate Manchester United.'
Grant has until May 28 to reply.