The basketball player began dating Sinanaj several months after his high-profile divorce from Kim Kardashian.
He and Sinanaj have been embroiled in a bitter legal battle stemming from Humphries's claim that he is being extorted for money in return for silence from his former girlfriend.
Sources tell TMZ that Sinanaj became angry when Humphries stopped returning her calls, and later resorted to leaving angry messages with the athlete's friends.
In one such message, Sinanaj allegedly warned: "If he's going to play me like that, I have way more s**t I can put out."
Humphries and his legal team have allegedly handed the tape over to the FBI in the extortion case now launched against Sinanaj.
However, attorney Joe Tacopina, who represents Sinanaj, claims that there is no evidence of extortion on the recording. He said that his client's time with Humphries was a "substantial relationship" and that she is preparing to launch a defamation lawsuit of her own.
Humphries, 27, recently accused Sinanaj of prostituting herself out of the New York hotel in which she works.