Ferguson was the latest of Hughes' rivals to speak of their shock at the way he was forced to take control of his team in Saturday's 4-3 victory over Sunderland before being sacked and replaced by Italian Roberto Mancini immediately after the game.
"That is one thing I do not need to discuss, it is so obvious, that kind of behaviour is unacceptable," Ferguson told a news conference on Thursday when asked for his reaction to the treatment of Hughes.
"It doesn't matter whether you have lost 20 games or, as in the case of Mark Hughes, two games. There is a way to treat people, surely.
"But Christmas time seems to bring the worst out of directors. Sitting there throughout the game, knowing something was going on, must have been terrible.
"Mark had obviously realised it was his last game, it must have been a terrible position to be in. I think everyone was shocked, obviously. I spoke to Mark the next day and I could tell he was suffering."
Ferguson was confident, however, that Hughes - who played under him at Old Trafford - would recover from his turbulent 18-month spell at United's wealthy neighbours.
"Of course he will," said Ferguson. "He did a great job with Wales, which is not an easy job, a great job with Blackburn and he was the right man for Manchester City at the time."
DEPLETED DEFENCE
Ferguson, meanwhile, has been concentrating on his first team squad and will welcome back Brazilian brothers Fabio and Rafael for Sunday's Premier League trip to 17th-placed Hull.
United are also clinging to the hope that Wes Brown and Nemanja Vidic will be fit to add bodies to a depleted defence.
"Hull will be encouraged by the fact we have got defenders injured," said Ferguson, whose team have lost two of their last three league games. "They will certainly have a go at us.
"It's always a dogfight down at the bottom of the table and, as usual, there are six, seven or eight teams involved in that battle."
United officially welcomed the Senegal forward Mame Biram Diouf this week after his work permit came through following his move from Norwegian club Molde.
However, it will be well into next month before he is able to play with his international clearance not expected until after the third round FA Cup match against Leeds on January 3.
"Hopefully, we will get his international clearance by the (Manchester) City (Carling Cup) semi-final (first leg on Jan. 6)," said Ferguson. "I don't want him to start that game, it will be too early for him but he has been terrific in training with us."
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