The US airman is said to be in a stable condition following the incident in a busy nightspot in Sacramento, California.

Air Force Times confirmed Mr Stone was stabbed four times in the chest.

"A1C Spencer Stone has been transported to a local hospital, and is currently being treated for injury," Air Force spokesman Lieutenant Colonel Christopher Karns is quoted as saying.

"The incident is currently under investigation by local law enforcement. He is currently in stable condition."

There is no evidence to suggest the incident was connected to Mr Stone's actions in France.

It was initially thought Mr Stone would not survive and a homicide investigation was launched, according to KCRA-TV.

Mr Stone was hailed as a hero in August after subduing a heavily armed gunman on a train heading from Amsterdam to Paris.

Speaking at the time, he recalled seeing the attacker in his carriage with an assault rifle "that looked like it was jammed".

He and friend Alek Skarlatos charged at the gunman and tackled him to the ground.

Mr Stone was stabbed with a bolt cutter in the neck and was sliced in the hand.

The pair, along with their other friend, Anthony Sadler, started punching the gunman.

Mr Stone recalled: "He seemed like he was ready to fight to the end. So were we."

The airman was eventually able to "choke him unconscious" and Mr Skarlatos hit him in the head with one of the guns, before he was tied up.

Mr Stone, who was also praised for helping to stop the bleeding of a wounded French-American passenger, said his thumb had to be reattached following the incident.

The three heroes, along with Briton Chris Norman, were awarded France's highest honour, the Legion d'Honneur, for their bravery.