Investigators in Saudi Arabia were on Sunday probing the possible motives behind an attack on a Canadian citizen, which came one week after the shooting of a Dane.

"We're still trying to figure out what the motive is," a source familiar with the situation told AFP.

The official Saudi Press Agency, citing police in Eastern Province, said the attacker used "a sharp object" against the Canadian while he shopped at a mall in the Gulf coast community of Dhahran on Saturday.

Police arrested a Saudi national, SPA reported, without giving a possible motive.

The Canadian, whose name has not been released, was in hospital after what the source described as a stabbing.

Reasons for the attack could include a workplace-related incident, political motives, or perhaps it was the work of a "crazy" person, the source told AFP.

A video posted on YouTube purported to show a trail of blood on the shopping centre floor, and the victim later sitting on a chair with his pants bloodstained.

The video was later "removed by the user," a notice said.

"Everybody's wondering what this means" after the shooting of the Dane on November 22 and a previous fatal attack on an American.

"Is there a trend line?" asked the source, requesting anonymity.

The Dane was shot in the shoulder "from an unknown source" as he drove away from his workplace in Riyadh last weekend, SPA said at the time.

He is still in hospital, the source said.

Riyadh police said the interior ministry was now handling enquiries about the Dane's case, but the department's spokesman said there was no new information available.

In October, a Saudi-American former employee of a US defence contractor shot dead one American colleague and wounded another in Riyadh.

The suspect had recently been fired from his job, officials said.

That was the first deadly attack on Westerners in Saudi Arabia since several were killed in a wave of Al-Qaeda violence between 2003 and 2006.

Since September, Saudi Arabia, the United Arab Emirates, Jordan and Bahrain have taken part in a US-led campaign of air strikes against the Islamic State (IS) extremist group in Syria, raising concerns about possible retaliation in the kingdom.

Canada and Denmark are among the countries -- with Australia, Belgium, Britain, France and the Netherlands -- participating in a similar campaign against IS in Iraq.

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