Deehan was escorted from Loftus Road shortly after the dismissal of the United player, Petr Kachuro, having previously been warned to remain in the dug-out by a female police officer. He was arrested for using "threatening words and behaviour", an offence under the Public Order Act, and must report back to the police on 17 December.
United's player-manager, Steve Bruce, said: "I'm delighted with the win but horrified that my assistant manager is down at the police station.
"He has been arrested seemingly for swearing - but there were thousands of people swearing out there today."
Bradford City's pounds 1m former Port Vale striker, Lee Mills, also found himself in trouble, and may face a Football Association charge after the 2-1 defeat at Huddersfield Town.
Mills confronted an assistant referee as the players left the field at the end of the game. The referee, Eddie Wolstenholme, is to report him to the FA.
Barnsley's manager, John Hendrie, expressed his determination to keep hold of Ashley Ward, a target for Leicester City, after his side's 3-2 win at Sunderland inflicted a first defeat of the season upon the First Division leaders.
Ward scored Barnsley's opener, missed a penalty - but was then sent off. "We have a valuation on him and, if someone meets it, we will have to consider the offer," said Hendrie, who turned down a pounds 3.8m bid from Leicester last week. "But I do not want him to go, it's as simple as that." Darren Barnard, with a penalty eight minutes from full time, hit the Tykes' winner.Reuse content