Spencer Stone, hailed as a hero after a French train terror attack,has been stabbed in Sacramento, California.
He is currently in a stable condition and is being treated at a local hospital, an Air Force official confirmed to the BBC.
CBS News first reported that he was "stabbed repeatedly" on a Sacramento street corner on Thursday morning.
Mr Stone, 25, is one of three Americans that helped to thwart a terror attack against a French train in August.
They were hailed as heroes for tackling a man who was carrying a Kalashnikov rifle, an automatic pistol with ammunition clips and a box cutter knife,
The men, assisted by other passengers, threw him to the floor of the carriage, removed his guns and restrained him.
Mr Stone and the two others, Alek Skarlatos and Anthony Sadler, were greeted as heroes upon their return to the US.
They received awards from Secretary of Defense Ashton Carter and met President Barack Obama at the White House.