Man, 18, accuses former USA Gymnastics doctor Larry Nassar of abuse, joins civil lawsuit Jacob Moore said in 2016, the disgraced doctor performed a treatment on him.

In April 2016, a 16-year-old gymnast at a critical point in his career, on the verge of making nationals, but with a nagging pain in his shoulder visited the home of a family friend and doctor for help.

"I went to Larry, thinking that I was going to get some legitimate medical treatment," 18-year-old Jacob Moore told ABC News today. "I got nothing even close to that."

On Monday, Jacob Moore, alongside his lawyers, announced that he'd joined more than 250 accusers in a civil lawsuit against Larry Nassar, the disgraced USA Gymnastics physician currently in prison for abusing hundreds of women and children.

USA Gymnastics, Michigan State University and others are also being sued.

Jacob Moore's story was first shared by his sister Kamerin Moore, who spoke of her own abuse at the hands of Nassar in a victim impact statement during his sentencing in January.

Kamerin Moore told the Michigan courtroom that she began seeing Nassar for treatment at the age of 10 when she suffered an injury performing gymnastics. She said shortly after her father died when she was 12, Nassar began molesting her.

In her statement, Kamerin Moore said Nassar became the "only adult male figure" in her life after her father's death.

"You weren't just a doctor to me, you were my buddy, but it wasn't long after our friendship developed that you decided what we now call 'your special treatment,'" she said. "My whole family was fooled by you."

She then said that Nassar had also molested her brother Jacob Moore after he'd injured his shoulder while doing gymnastics.

Jacob Moore, currently a freshman at the University of Michigan and on the gymnastics team, said that in April 2016, he was a member of USA Gymnastics and suffering from a shoulder injury. One day, after practice, he, Kamerin Moore and their mother went to Nassar's house. Jacob Moore said that he had been to the house for medical assistance once or twice before.

"He was pretty good friends with, you know, my whole family," he said. "He just seemed really trustworthy."

Jacob Moore said Nassar had exam tables set up in the basement that evening. Jacob Moore, who said he was not wearing a shirt, laid on a table and Nassar started putting acupuncture needles in his shoulder.

"He pulled my pants down on one side, partially exposing me," Jacob Moore said during a news conference Monday. "Slowly he would work his way with acupuncture needles towards my inner groin."

Jacob Moore said a young woman, whom he identified as a "victim" of Nassar's, was also in the room.

His lawyer Ven Johnson told ABC News today that Nassar exposed Jacob Moore's genitals to the young woman, all while "explaining how chi from the shoulder is related to chi down in the area of the groin."

"A lot of these young people like Jacob or Kami [Kamerin] would go to him [Nassar] with a specific pain or an issue in a particular part of their body. Larry would run this manipulative B.S. on chi and energy," Johnson said.

Jacob Moore said he felt uncomfortable at the time but believed the doctor was healing his shoulder.

"The amount of trust that I had in him, kind of, lead me away from thinking that something was actually wrong with the situation," he said.

Nearly two years later, he said, he started learning of the allegations against Nassar. Jacob Moore said neither he nor Kamerin Moore had spoken to each other about their alleged abuse at the hands of Nassar until one day, when the two siblings were having lunch with friends.

He said it was then that he decided to research the treatment he'd received in 2016. Jacob Moore, who eventually had to have surgeries on both of his shoulders, said he found nothing.

"I immediately was very shocked and almost angry," he said.

Nassar pleaded guilty last year and was sentenced to up to 175 years in prison in January on seven counts of criminal sexual misconduct in the first degree.

After the sentencing, the entire board of USA Gymnastics resigned under pressure from the U.S. Olympic Committee. Also, the president and athletic director of Michigan State University, where Nassar worked for decades, stepped down.

In two other cases, Nassar was sentenced to 60 years in prison for possession of child pornography in December 2017 and 40 to 125 years in prison for three more criminal sexual conduct cases in early February. He pleaded guilty in both of those cases as well.

USA Gymnastics told ABC News today it would not comment on the complaint filed by Jacob Moore.

"USA Gymnastics supports our athletes, like Aly Raisman, Jacob Moore and others, who have shared their experiences with abuse, and we are very sorry that any athlete has been hurt by the despicable crimes of Larry Nassar. USA Gymnastics first became aware that an athlete had expressed concern about a procedure by Larry Nassar in June 2015, which led USA Gymnastics to report Nassar to the FBI and dismiss him from further involvement with USA Gymnastics. USA Gymnastics is committed to doing everything we can to prevent this from happening again by making bold decisions and holding ourselves to the highest standards of care. We need the gymnastics community to join with us to accomplish this for both the young men and women who are pursuing their gymnastics dreams today and to honor those who have gone before," the organization said in an email.

MSU and Nassar's lawyers did not respond to requests for comment.

Jacob Moore said that the stigma surrounding men who have suffered sexual abuse is wrong and that men should be given a platform to come forward and share their stories. He said for now he's focusing on gymnastics and trying to leave the past behind him.

"If I allow him [Nassar] to kind of take away that love for the sport, I see that as kind of him winning. ... That's the last thing that, you know, any of us want," he said.

Each accuser is seeking unspecified monetary damages.

ABC News' Kayna Whitworth, Katherine Carroll, Bill Hutchinson and Darren Reynolds contributed to this story.