A disabled Vietnam veteran has filed suit against the suspended NYPD detective who was accused last week of masturbating while peeping through children’s windows — claiming the disgraced cop attacked him, maced him and arrested him without cause last year.

Sylvester Wilson, who walks with a cane, said he came upon the alleged serial pervert detective, Robert Francis, in June 2016 as the now-suspended cop was issuing a summons to the driver of an illegal “dollar van,” according to the Brooklyn federal court lawsuit filed late Wednesday.

The 67-year-old vet, who lives in Prospect Heights, Brooklyn, says he didn’t know the driver but intervened on behalf of him because he thought the guy deserved a break.

Wilson says he told Francis, “He is a hardworking person. What you are doing is wrong” — which the papers say prompted the cop to shove the man in the chest and knock him to the ground before walking away.

Wilson, who also lives with a heart condition, says he went to the local precinct to report the cop but was told that without a name or badge number, he was out of luck.

About three months later, Wilson came upon the detective again in Fort Greene, Brooklyn, and attempted to take a picture of his badge, but Francis covered it with a newspaper and walked into a nearby clothing store, according to the lawsuit filed by attorney Alexander Dudelson.

Wilson hobbled after him into the store, where Francis sneered, “Now you are trespassing,” grabbed him, dragged him outside and blasted him with pepper spray before cuffing him and throwing him into his marked police car, the suit says.

The vet was later arraigned on trespassing and other charges, after Francis filed a phony report saying Wilson had spit on him and “flailed” during his arrest, the suit claims.

The charges against Francis were eventually dismissed. The case was sealed in January by the Brooklyn DA’s office, but Wilson still says he suffered irreparable injury and humiliation due to Francis’ actions.

“There was no reason for what he did to an innocent person like me, to assault me the way he did,” an emotional Wilson told The Post on Thursday.

“I could have spent 10 to 20 years in jail,” he said, tearing up at the thought.

Still, Wilson said he was “shocked” to hear of the perverted allegations against Francis.

“He doesn’t deserve to be a detective,” the veteran added. “He is not fit as a person who serves the public.”

The suit which also names the city for hiring Francis cites excessive force, false arrest, and malicious prosecution.

“We have not seen the suit,” a city Law Department spokesman said. “It will be reviewed once we are served.”

A phone number for Francis was not in service. No lawyer was listed for him on court documents.