Posh are bottom of the Championship, nine points adrift of safety, having won just three times in the league this season.
Darren Ferguson, the manager who had guided them to two successive promotions, parted company with the club in November and was replaced by Mark Cooper.
In a lengthy statement on the club's official website, MacAnthony said: "I have to apologise to all Posh fans for this season up until now and for all the events on and off the field. It has been nothing short of a disaster and I can of course understand their frustrations.
"I am done with defending the players, previous management, current management and everyone else at the football club top to bottom.
"Nobody has been good enough this season and we have failed our fans in the worst possible way and this has resulted in us being bottom of the league and heading for League One in a hurry.
"I promise the fans this will be the last time I speak in the press this season, but some home truths need to be told and as always I like to be honest with the fans and as open as possible."
He added: "The team spirit from the last two years has nearly been destroyed by greed, skulduggery, tapping up and disloyalty from within and this has all occurred over the last 120 days or so, non stop and is eating away at our inner core."
MacAnthony hinted he was unhappy at Ferguson, now Preston boss, trying to tempt his players away.
"Every week brings another drama and it usually involves an ex-manager, a current team member and the promise of bigger wages followed by a derisory £100k bid and all this after the player has been unsettled and offered terms behind our back," he said.
"Ask him (Ferguson) why in the last seven days he has offered terms to some of our players without agreeing terms with our club for them and of course totally unsettling these players."
Peterborough host Preston in the Championship this evening.
The chairman also had harsh words for the club's players, telling them to "grow up".
He added: "They repay the club with below par performances, temper tantrums off the field and making it clear they no longer want to play for our club when the going gets tough. Well it's time for all of these players to grow up and act like professionals."
Coca Cola Championship. Click here to bet.