"All they get to do is write a report," Giuliani said, according to the network. "They can't indict. At least they acknowledged that to us after some battling, they acknowledged that to us."
A spokesman for Mueller, Peter Carr, did not immediately respond to a Reuters request for comment.
Mueller is investigating allegations that Russia interfered in the 2016 US presidential election and possible collusion between Moscow and the Trump campaign.
CNN said the Mueller team had been debating whether to challenge the Nixon-era guidelines, which were reaffirmed during the Clinton administration, that a sitting president cannot be indicted.
Giuliani and another Trump lawyer, Jay Sekulow, did not immediately respond to a request for comment from Reuters.
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