Ferguson, preparing his team for Sunday's FA Cup Final against Everton at Wembley, resumed hostilities with Benitez during his press briefing at United's Carrington training ground on Friday lunchtime.
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But Ferguson's latest attack came in defence of close friend Allardyce who, according to the United manager, was treated with 'contempt' by Benitez during Liverpool's 4-0 victory over Blackburn at Anfield last Saturday.
Ferguson said: 'There is one thing about the arrogance he has shown, but the thing you can't forgive is his contempt to Sam Allardyce last week when Liverpool scored their second goal.
'Did you see it? He gestured to suggest that the game was finished. Absolute contempt. I don't think Sam Allardyce deserved that, a guy who has worked so hard for the LMA (League Managers Association).
'He didn't deserve that. Having had to play with a weakened team, he didn't deserve to get that kind of contempt.
'I don't think any other Liverpool manager would have done that. It was beyond the pale.'
Allardyce also hit out at Benitez, accusing the Spaniard of being "disrespectful" for what he claims was a "humiliating" gesture.
For total clarity, Allardyce has reviewed footage of the incident several times after initially witnessing it following Liverpool's second goal of a 4-0 victory at Anfield last Saturday.
Although Benitez is well-known for his hand signals from the technical area, Allardyce insists the gesticulations following Fernando Torres' 33rd-minute header were directed towards him and his team.
Allardyce's understanding is that Benitez crossed his arms over dismissively as if to suggest 'that's it, game over, job done'.
The Rovers manager also believes Benitez showed a further lack of respect by not showing up in his own office for a post-match drink, leaving Allardyce seeking an explanation.
"I think if everybody has a look back at his gestures you will see them as pretty dismissive to me and the Blackburn Rovers team as a whole," fumed Allardyce.
"I was hugely disappointed by those gestures. I think they were disrespectful and quite humiliating. Having looked at them again this week, I think I'm right and everybody will see why I'm complaining.
"The feeling was that he had written us off. It was open arms and then a crossover of the arms as if to suggest that was it.
"I admit it was a hard game, a difficult game for us, and we were well beaten by an outstanding Liverpool side. But in terms of respect, you don't expect those sort of things to happen in a game of football. I was very, very upset by it.
"The game is hard enough as it is without a fellow manager doing what seemed to be an undermining gesture. I then waited to have a word with him after the game in his room, but as usual and unfortunately, he didn't turn up.
"Not explaining himself by not turning up in his office really shows what he is like. The only people I saw were Sammy Lee and a few of the staff, but he never showed his face. That was just as disappointing as the gesture, and it typifies the man."
There has never been any love lost between the two men in the past, with Allardyce's outburst merely serving to add fuel to the fire.
Allardyce has made no attempt to contact Benitez this week to try and clarify the matter, insisting: "Why should I?
"If he can't come into his own room and have a drink with his fellow manager, why would I want to pick up the phone and speak to him?
"I gave him the opportunity by being courteous enough after being beaten 4-0 to go and have a drink in his room.
"There was no need for those sorts of gestures, and my opinion as to whether I'm right is obviously going to be speculated upon by other people, but I think I'm right.
"He would have had the opportunity to have explained himself if he had turned up in his room, but didn't, so that's why I'm talking about it today.
"It's in the past now and I'll move on, but I just want to make everybody aware of what I consider to be a lack of respect for me, the Blackburn Rovers players and the football club as a whole."
With United up against Liverpool's Merseyside rivals Everton on Sunday, Ferguson admits that even David Moyes's team have been forced to endure the 'arrogance' of Benitez.
He said: 'Irrespective of what Rafa Benitez says, Everton are a big club. He called them a small club, which just points to his arrogance.
'David Moyes is building a big club with a young squad that will get better. He has a good variety there, so I think he has done a great job.
'We are facing a very hungry team on Sunday because David has to win a trophy and I know he is feeling that way.
'This is a big opportunity for him, so we know what we are up against.'
Michael Carrick (ankle) and Wayne Rooney (foot) are expected to be fit on Sunday, while Gary Neville and Rafael da Silva are due to contest the right-back role.