Larry Rudolph, who has managed the singer's career for 25 years, said in a letter released to media outlets late on Monday that he had become aware that Spears had been "voicing her intention to officially retire."
"As her manager, I believe it is in Britney's best interest for me to resign from her team as my professional services are no longer needed," Rudolph said in the letter, which was sent to Spears' father Jamie and her co-conservator Jodi Montgomery.
Spears (39) has not performed in public since her last world tour ended in October 2018.
In explosive testimony last month, she told a Los Angeles judge that a 13-year court-approved conservatorship that has controlled her personal and business affairs was abusive, and said she wanted to take back control of her own life.
She has yet to file the formal documents needed to start that process.
Celebrity media website TMZ.com said on Tuesday that attorney Samuel Ingham, appointed to represent the singer's interests in the legal arrangement, was planning to file papers asking to be dismissed from his role.
Spears told the judge in June that she wanted to choose her own attorney.
Ingham did not respond to a request for comment.
The singer's testimony last month has thrown the conservatorship into disarray.
Both Jamie Spears and Montgomery have denied responsibility for some of the problems she complained about, while Bessemer Trust, the financial company that was chosen last year to help manage her business affairs, has also asked to be removed.
The next court hearing in the conservatorship is due to take place next week.
