A US airman hailed a hero for helping to stop a terror attack on a French train has been stabbed and seriously wounded outside a bar in his home town, in what police said was an alcohol-related brawl.
Spencer Stone, 23, was knifed three times in the upper body and underwent two hours of surgery, said Dr Douglas Kirk, chief medical officer at UC Davis Medical Centre in Sacramento, California.
"This incident is not related to terrorism in any way," deputy police chief Ken Bernard said. "We know it's not related to what occurred in France months ago."
A grainy surveillance video from a camera outside a Sacramento off-licence showed a man who appeared to be Stone fighting with several people at a junction. The group spilled into the street as people took swings at each other, and one person got knocked down.
Police said two assailants fled in a car. No immediate arrests were made.
The Sacramento stabbing happened in a busy area ringed with bars and restaurants that is a popular nightlife magnet for young people and is generally considered safe.
Mr Bernard said Mr Stone was out with four friends when they got into a fight with another group of people. The deputy chief would not say what sparked the argument. He said there was no evidence the assailants knew who Mr Stone was.
Mr Bernard said he did not know whether Mr Stone was drinking, but others in his group were.
Dr Kirk said Mr Stone remained heavily sedated in the hospital's intensive care unit. He declined to discuss any details about the surgery or whether any vital organs were damaged in the stabbing, beyond saying Mr Stone had "significant injuries".
The airman arrived at the nearby hospital conscious despite his wounds, the doctor said.
"I suspect given his history of recent events he is quite a fighter," he said.
He said Mr Stone's family asked him to convey "their deepest gratitude for all the expressions of concern for his welfare at this very difficult time for them".
In August, Mr Stone and two of his childhood friends from Sacramento, national guardsman Alek Skarlatos and college student Anthony Sadler, were on holiday in Europe when they sprang into action aboard a Paris-bound passenger train and tackled Ayoub El-Khazzani, a man with ties to radical Islam.
El-Khazzani had boarded the train with a Kalashnikov rifle, a pistol and a box cutter.
Mr Stone, who is assigned to Travis Air Force Base in California, had a severely cut thumb and a knife wound to his neck, received during the struggle with the gunman.
US president Barack Obama met the three Americans last month, praising them for their quick thinking and courage and calling them "the very best of America". They were also awarded France's highest honour by President Francois Hollande.
The three appeared on late-night talk shows and received a parade in their home town.
Mr Stone is the second of the three Americans to be shaken by violence at home since their return.
Last week, Mr Skarlatos left rehearsals for TV's Dancing With The Stars to rush back to Roseburg, Oregon, after a gunman killed nine people at the community college that he attends.
"It's honestly the strangest emotion I ever felt," Mr Skarlatos said in a taped segment on the show. "Even the train made more sense than this does. There's nothing you can do."
Mr Skarlatos tweeted on Thursday: "Spencer is one tough guy" and "Everybody send prayers out to the Stone family today."