The man charged in a machete attack on a suburban Hanukkah party could face the death penalty if a comatose victim dies from his wounds, a federal prosecutor said Monday.

Grafton Thomas, 37, didn’t react visibly when Assistant US Attorney Michael Krouse raised the potential of capital punishment in the high-profile case during a court hearing in White Plains.

In response to a question from Judge Cathy Seibel, Krouse said it was unclear whether everyone injured in last month’s bloodbath would survive.

“One of the victims does remain in a coma,” Krouse said.

“Other than that, we do not have a strong sense of that.”

The most seriously injured victim, 72-year-old Josef Neumann, suffered a machete wound that “penetrated his skull directly into the brain,” his family has said.

His youngest daughter, Nicky Kohen, told The Post on Monday that Neumann remained in critical condition at Westchester Medical Center

“The doctors can’t guarantee that he will wake up,” Kohen said.

“We hope when we say our names, give him a massage or touch, he hears us and is aware we are there. But from a medical standpoint, they don’t know.”

The specter of execution was raised following arraignment before a different judge at which Thomas pleaded not guilty to federal hate-crime charges that currently carry a maximum sentence of life in prison.

Thomas, who’s being held without bail, also told Magistrate Judge Paul Davison hat he was taking anti-psychotic and anti-depressant medication in jail.

Thomas — whose lawyer has said he was off his meds during the Dec. 28 rampage in Rockland County — appeared lucid and cogent while answering questions from Davison, including whether he was on any medication.

“As prescribed, I have taken Prozac, 20 [milligrams], and Latuda, 80 milligrams, at night,” Thomas said.

“Are you clear in your head as you stand here?” Davison asked Thomas, who wore orange and yellow scrubs and whose ankles were chained.

“I am, your honor,” Thomas replied.

Defense lawyer Michael Sussman waived a reading of the 10-count indictment handed up last week and entered not-guilty pleas to five charges each of attempting to kill people because of their religion and obstructing their free exercise of religion.

When asked by the judge if he thought Thomas “understands what he’s accused of,” Sussman said, “No, your honor.”

“He understands it to the extent he understands it,” Sussman added.

Outside court, Sussman called the potential for the death penalty “really a hypothetical situation” that Seibel raised “in an abundance of caution.”

Sussman wouldn’t detail why he doubted his client’s understanding of the charges, calling that “clearly an attorney-client privilege matter,” but said Thomas had undergone two examinations by defense psychiatrist, with a third planned.

Sussman said he would seek a competency hearing in papers he plans to file Jan. 27.

Thomas’ mom, pastor and several other relatives attended the court sessions but left without comment.

Thomas is accused of using an 18-inch machete to slash and stab at least five Orthodox Jewish men who were celebrating Hanukkah at their rabbi’s home in Monsey, with authorities alleging he kept journals that contain “anti-Semitic sentiments.”

Sussman has denied that Thomas was motivated by hate, saying he has a lengthy history of mental illness that includes psychosis and depression, with symptoms including auditory hallucinations.

Krouse said Monday that in addition to a bloody machete and knife found in Thomas’ alleged getaway car, authorities found another machete and knife in another car linked to him.

Sussman said of that discovery, “I don’t know anything about it or if it’s associated with anything.”

Also Monday, the Rockland County District Attorney’s Office released a copy of its indictment against Thomas, which newly elected DA Thomas Walsh announced Jan. 3.

The charges include six counts of attempted murder, involving one victim more than in the federal case.

The Rockland indictment also charges Thomas with three counts of assault, three counts of attempted assault and two counts of burglary.

The top charges carry a maximum sentence of 25 years in prison.