Published today (December 20), the PAC report described the settlement as a "cavalier" use of public money. It also took issue with the £4 million paid to ten departing senior managers since 2010.
"We have already taken legal advice about whether we could actually take any money back," Patten told BBC Radio 4's Today programme.
"If we hadn't done the settlement there and then we'd have had to do a more costly settlement with a constructive dismissal and probably an unfair dismissal on top of that.
"It would have taken time. To do that we would have to argue that on the basis of the Pollard report we would have been justified in summary dismissal. It is doubtful we could do that."
Entwistle left the BBC in the wake of the pulled Newsnight investigation into Jimmy Savile and the flawed edition of the same show which wrongly implicated Lord McAlpine in the North Wales abuse scandal.
Patten claimed that had the Trust battled over Entwistle's settlement in court, it could have cost a lot more.
He added of the BBC's current problems: "It's about bad management that has to be changed."
Patten said that three directors-general had left "because of cock-ups in the way we manage current affairs and journalism... we can't go on like that".