By former pro tennis star James Blake's account, the man approaching him in 2015 outside his hotel caused no alarm because he looked like an old high school buddy.

Blake found out the hard way that it was instead a plainclothes police officer who mistook him for a suspect in a fraud investigation.

On Tuesday, Blake testified at a police department disciplinary trial that the officer never identified himself before throwing him to the ground and handcuffing him. When police realized their mistake, said Blake, they released him without an apology from the officer.

"It shouldn't happen to me. It shouldn't happen to anyone," Blake testified. "There needs to be accountability for everybody."

Officer James Frascatore this year rejected a deal asking him to forfeit vacation days to resolve New York Police Department internal charges that he used excessive force. The NYPD administrative judge who's hearing the case will recommend a potentially more severe punishment, including dismissal from the nation's largest police force, to the police commissioner.

Frascatore, who denies he did anything wrong, also will take the witness stand. He has been assigned to desk duty pending a decision about his future.

The officer "looks forward to correcting the false narrative which has surrounded this case for two years," said his attorney, Stephen Worth.

Blake's arrest - captured in a security video - came at a high point of the national debate over police use of force against unarmed black men. The 37-year-old American, once the No. 4 tennis player in the world, is the child of a black father and white mother; Frascatore is white.

The NYPD has said that Blake matched a photo of a suspect sought in the case and that race wasn't a factor. But after the video was made public, city and police officials took the unusual step of apologizing and establishing in Blake's name a fellowship aimed at helping people who accuse police of abuses to get full reviews by a police oversight agency.

Blake, in his new book about sports and activism, "Ways of Grace," describes going from peacefully waiting for a ride to that year's U.S. Open tennis tournament to finding himself with his "face pressed to the concrete." Fearing he could make things worse by resisting, Blake told himself to cooperate until the officer pulled him up.

"This is an absolute mistake," he recalls telling the officer. "You have the wrong person."

The half-dozen officers at the scene did little to check out his story until an officer who appeared to be a supervisor showed up several minutes later and let him go, Blake says.

Humiliated, his first instinct was to let it go before his wife asked him what he'd do if the same thing happened to her.

"That's when I got angry," he writes.

Responding to reports of the encounter, the NYPD initially added insult to injury by claiming Blake had only been detained for a couple minutes and was never manhandled or handcuffed, he says. He decided to seek out hotel security, which showed him the video proving he was slammed down and kept cuffed at least 10 minutes.

The next day, he decided to speak out about the incident on "Good Morning America." And now, he is using his book to share his takeaways.

"It should not matter that I'm a tennis star ... to be treated respectfully and not have my rights taken away from me from law enforcement," he writes.

His case, he adds, "speaks to a larger issue in America - the use of excessive force by law enforcement, especially against minorities."