WASHINGTON — A member of President Trump’s legal team said on Sunday that the president was not under investigation by the special counsel looking into Russia’s election-year meddling, contradicting Mr. Trump’s assertion in a Friday morning tweet that he is a subject of the widening inquiry.

The denial on Sunday by Jay Sekulow, one of several personal lawyers Mr. Trump has hired to represent him in the Russia case, is the latest of many examples in which the president’s aides and lawyers have scrambled to avert a public-relations mess created by Mr. Trump’s tweets, off-script remarks or leaked private conversations.

Advisers have been forced to perform postpresidential cleanup in the wake of Mr. Trump’s tweet claiming he had been wiretapped by the Obama administration, his Oval Office comments to Russian diplomats about the former F.B.I. director, his private musings about the possibility of firing the Russia special counsel, his suggestion that there might be recordings of White House conversations, and his comments about a “military” deportation operation.

In Mr. Sekulow’s case, his appearance on multiple Sunday morning talk shows took on the added urgency of trying to protect his client from admitting that he is in legal jeopardy during a criminal investigation, one that appears to be increasingly focused on whether Mr. Trump took steps to interfere with the normal progress of the federal inquiry.