Washington (CNN) President Donald Trump's lawyers are preparing for a legal showdown with special counsel Robert Mueller, according to sources familiar with their thinking.

Trump's legal team is bracing for the dramatic possibility that Mueller would subpoena the President, setting up a collision that could force a lengthy court fight and test the legal limits of the President's power all the way up to the Supreme Court.

Mueller has raised the possibility of a presidential subpoena in at least one meeting, according to two sources. But some of the President's legal advisers are gambling that Mueller would not go that far. The Washington Post first reported on the subpoena threat.

The already slim chances of Trump sitting for a voluntary interview with Mueller's investigators are growing dimmer, sources close to the President say.

Asked whether the President would ever plead the Fifth Amendment to avoid answering questions, two sources said the legal team believes there are many "constitutional challenges" that would need to be met before that possibility even would be considered.

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