The chairman of the BBC Trust says the corporation may have to "do less" as it tries to meet budget cuts.
Sir Michael was speaking after his first 100 days as chairman
Sir Michael Lyons said the BBC faces "tough decisions" after the government imposed a lower than expected licence fee settlement.
He would not discuss specific changes, but there has been speculation in the press that services could close down.
Sir Michael also said the Trust could take further disciplinary action over misleading footage of the Queen.
A trailer for a fly-on-the-wall documentary about the Royal Family was presented by BBC One controller Peter Fincham at a press launch earlier this year.
Sir Michael was asked by the Times newspaper whether Mr Fincham should have personally checked the veracity of the clip.
"Do I personally think it was reasonable to check something that was so newsworthy? Yes, I do," he said.
Speaking to the Daily Telegraph, he said the incident "had a very powerful effect across the country as a whole and [has] done the BBC no good at all".
He added the BBC Trust would not make a judgement on the affair before it received a full report later this year.
"I personally do not want a few sacrificial lambs pulled out and slaughtered in the belief that we'll all feel better as a result."
The documentary appeared to show the Queen storming out of a photo session with Annie Liebovitz, but it was later revealed the footage had been edited out of sequence.
Sir Michael gave several interviews on Wednesday to mark his first 100 days as chairman of the BBC Trust.
The body replaced the BBC governors earlier this year and is the broadcaster's ruling body.
Its job is to represent the views of the public, not those of the BBC management.
Misleading footage of the Queen had damaged trust, Sir Michael said
Sir Michael, a former market trader, stated several times that the BBC may have to make sweeping changes in order to cope with its reduced income.
"The BBC Trust will be saying very clearly that we don't want the BBC to be doing more than it can do very well," he told the Daily Telegraph.
"Have we ruled out radical changes? No, we haven't.
"I don't want to give you the impression that this is code for 'there are definitely going to be some changes,' but it is about what you can afford to do with the money you've got."
Director General Mark Thompson has already presented the BBC Trust with an initial range of options for how to reprioritise its spending, but Sir Michael would not be drawn on the plans.
He expressed confidence in Mr Thompson's ability to steer the corporation through a period of change, and to weather the storm over trust in the BBC.