An FA spokesman said Wednesday, per talkSPORT:
We are looking into David Moyes' comments to the media following the match at Sunderland.
We are also contacting both clubs to seek their observations in relation to the use of flares last night.
A picture of one of the flares allegedly set off by United fans was posted by the Instagram account of theawaydayfans:
While Fabio Borini's penalty illuminated the Stadium of Light and thrust the Black Cats to a 2-1 victory over their visitors, the travelling support appeared to call upon the use of flares to show their support, per David Kent of the Daily Mail Online:
"Flares were lit in the away end at the Stadium of Light, with some being thrown into a section of home fans," writes Kent.
As reported by Richard Wheatstone of the Manchester Evening News, at the beginning of December 2013, figures released by the UK Football Policing Unit indicate the Red Devils "top a Premier League table of incidents involving fans lighting flares during the current season."
The most recent incident is not the first time a Capital One Cup tie featuring United has involved flares this campaign. Liverpool fans were said to have launched similar abuse toward their Manchester counterparts during their trip to Old Trafford Sept. 25 of last year, per The Telegraph's Mark Ogden.
Although fans produced plenty of spark away from the Stadium of Light pitch, United's third loss in a week has many questioning the credentials of David Moyes, and indeed, his players.
The probing qualities of Adnan Januzaj, who played exciting football from a central position, and the hard work of Danny Welbeck, were perhaps the only outfield performances exempt from criticism during United's visit to Wearside.
Both sides enjoyed spells of domination throughout the match, but Gus Poyet's side snatched an advantage through Ryan Giggs' own goal and Borini's penalty, which was awarded after Tom Cleverley fouled Adam Johnson on the cusp of his own area.
As tweeted by ESPN, Moyes complained about the referee Andre Marriner's performance after the match:
The manager's tough start to the season doesn't seem to be getting easier. Moyes is unlikely to gain many fans by continually complaining about officials—he also criticised Howard Webb after United's loss to Spurs, per Adam Crafton of the Daily Mail Online—even when his team appear to be unfortunate.
United's more pressing concern is the form of a squad that looks terribly underpowered at this stage of the season. With Wayne Rooney and Robin van Persie among those sidelined through injury, Moyes has limited quality to call upon during this busy time.
He may be tempted to strengthen his squad throughout the January transfer window and could see his frustration disappear if some of his reported £200 million budget is spent on world-class players, per Chris Wheeler of the Daily Mail Online.
United's next match comes Jan. 11 in the must-win Premier League tie against Swansea.
Having already lost at home to Michael Laudrup's team in 2014, Moyes and his men need to capture three points if they are to continue battling for a place in next season's Champions League.