A woman set to testify that Sean “Diddy” Combs coerced her into sexual acts may not take the stand, the feds say — possibly delivering a blow to the high-profile prosecution before a jury is even seated.

The witness, dubbed “Victim-3” in court papers, had been expected to tell jurors that Combs “sexually exploited” her during his alleged decades-long reign of sexual terror, prosecutors say.

But the prosecution team admitted during jury selection this week that it’s been having trouble contacting the person or her lawyer, who has been dealing with undisclosed “personal issues.”

“We do not know whether she intends to appear, and we are trying very hard to find out because we are having trouble communicating with her counsel,” prosecutor Maurene Comey said Wednesday when pressed to provide an update on the situation.

Comey, who also worked on the prosecution team that convicted Jeffrey Epstein’s madam Ghislaine Maxwell, told the court on Monday that the witness “does not live locally” and “may not show up, even if we try to enforce the subpoena and want to call her.”

The potential pre-trial issue comes just a week after the feds said that they had spoken with the woman’s lawyer and learned that the accuser planned to use her real name during her testimony, rather than the pseudonym she had previously asked to use.

Prosecutors promised to provide another update on Friday morning, when a jury of 12 New Yorkers is expected to be finalized in the bombshell racketeering and sex trafficking case.

The feds still have three more alleged victims set to testify, including Combs’ ex-girlfriend, R&B singer Cassie, and two women who will testify under pseudonyms, according to court records and sources.

A fifth accuser will be allowed to testify as well — even though Combs is not specifically charged with any crimes related to her — because her account mirrors the coerced sex accusations of the other victims, according to a recent ruling by Judge Arun Subramanian.

The “I’ll Be Missing You” rapper, 55, is accused of helming Bad Boy Records as a “criminal enterprise” that abused and assaulted women, carried out kidnappings and at least one arson, and paid bribes to cover up its illicit acts.

Among the eye-popping allegations jurors will hear are that Combs forced his ex-girlfriends into drug-fueled, days-long sexual “performances” he called “Freak-Offs,” in which Combs would masturbate while his partners had sex with male sex workers.

He has pleaded not guilty to charges that carry a maximum sentence of life in prison.