The FA is investigating David Moyes' latest criticism of referees, following Manchester United's defeat by Sunderland in the first leg of their Capital One Cup semi-final.
Moyes claimed the Old Trafford side were "playing referees as well as the opposition".
The Scot had described a decision not to award United a penalty as "scandalous" after an earlier defeat by Tottenham Hotspur. Moyes could now face disciplinary charges.
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The Capital One Cup tie is also under scrutiny by the FA after a number of flares were set off during the match. "We will contact the clubs to seek their observations in relation to the use of flares," said a FA spokesperson.