Let's say a client confesses one thing to their lawyer, but at trial makes a radically different claim when asked while under oath. The difference is substantial and likely to affect the result of the trial and the lawyer reasonable believes the defendant has committed perjury.
He can't come out and accuse his client of lying based off of confidential information covered by attorney client privilege. However, he also can't support perjury, putting him in an awkward position.
Does the lawyer just move on and say nothing? Can they continue their planned defense as it was because the perjury doesn't change the argument, even if it could affect the odds of the client being found guilty? Then again what if the perjury does change the argument the defense was planning to make and he has to either alter his plan for defense or likely reveal the perjury? If the lawyer adjusts his defense in deference to the lie is he not supporting perjury?
Does the lawyer simply say he can't continue to defend his client and ask for a mistrial without saying why?