US airman Spencer Stone, who helped subdue an attacker on a French train in August, is in a stable condition after being stabbed in California, a US air force spokesman said.
Mr Stone is being treated in a hospital in the Sacramento area, said Lt Col Christopher Karns, who added that details are sketchy.
Mr Stone is assigned to Travis air force base in California.
Lt Col Karns said the matter is being handled by local law enforcement officials.
He had no details on the nature or exact location of the stabbing.