Robert F. Kennedy Jr. has filed paperwork to withdraw from the presidential race in Arizona, a spokesman for the Arizona secretary of state’s office said on Thursday night.

The move comes a day before Mr. Kennedy, an independent candidate, is set to give an address in Arizona about the future of his struggling campaign.

He is expected to end his candidacy, and possibly to endorse former President Donald. J. Trump following weeks of discussion between their camps, although people close to Mr. Kennedy say an endorsement is not yet certain.

A spokeswoman for the campaign did not immediately respond to a request for comment.

Just last Friday, Mr. Kennedy had submitted 118,000 signatures to qualify for the Arizona ballot, more than the required amount, said Aaron Thacker, the spokesman for the secretary of state’s office. Mr. Kennedy was verified by the secretary of state’s office to appear on the ballot this week.

“In fact, when he filed Friday, our staff spent the entire weekend working to verify his signatures,” Mr. Thacker said. “He only needed about 42,000, and he got over 118,000.”

Those signatures, however, could be problematic. As The New York Times reported this week, two people familiar with the campaign’s operations said the signatures had been collected by a super PAC backing Mr. Kennedy, rather than the campaign itself. Federal law limits coordination between campaigns and outside organizations, and the move would most likely have opened the campaign up to legal complaints.

Mr. Kennedy began his presidential campaign last year as a Democrat, challenging President Biden. He later embarked on an independent campaign that unnerved both major parties, which feared that he would siphon critical support from their candidate.

In recent weeks, as his campaign’s money ran low, Mr. Kennedy’s support in national polls, once in the low double digits, plunged to about 5 percent. It was nowhere near sufficient to have a shot at victory, but still enough to potentially affect the results of the election, depending on his numbers in key swing states.

Mr. Kennedy spent much of his career working as an environmental lawyer but became known in recent years for his opposition to vaccines and for his promotion of conspiracy theories and right-wing misinformation. Many members of the Kennedy family condemned his candidacy and took to the campaign trail this year to support Mr. Biden’s re-election.

This is a developing story and will be updated.