Saudi security forces are currently hunting the gunmen who fired at Gardner, 42, and Simon Cumbers, 36, on Sunday with a machine pistol.
The pair were filming the house of an al-Qaeda militant in the al-Suwaydi suburb of the Saudi capital Riyadh alongside a government minder when they were shot at from a passing Jeep.
Cumbers died at the scene. Gardner - an expert on al-Qaeda - was rushed to the nearby Iman Hospital where he underwent several hours of surgery to remove two bullets from his abdomen. He was later moved to the King Faisal Specialist Hospital where he is being guarded by special forces.
His condition is described as stable but critical.
Riyadh's police chief has said "unknown elements" were responsible for the attack, but reports have linked the gunment to al-Qaeda.
The men's government minder is believed to have escaped unharmed and is now being questioned.
The two journalists travelled to Saudi Arabia last week after terror attacks in the city of Khobar which killed 22 people.