A Canadian-Israeli dual citizen injured in a deadly attack on a Jerusalem synagogue has been upgraded to serious condition after undergoing an operation Tuesday.

Howard Rotman, 53, suffered stab wounds to his head, eyes and arms Tuesday, after two Palestinian cousins armed with knives, cleavers and a gun stormed a synagogue in Jerusalem.

Five people died in the attack, including four worshippers and an Israeli policeman. At least five other people were injured. The two assailants, identified as cousins Ghassan and Oday Abu Jamal, were killed by police during a shootout.

On Wednesday, a hospital spokesperson said Rotman had been operated on and is now sedated and on a respirator, CTV's Daniele Hamamdjian reported from Israel. His condition was upgraded to serious.

Toby Trompeter, a long-time friend of Rotman, described the father of 10 as "good-natured" and "kind."

"He's just always with a smile on his face, and always seemed to be looking for the humour in a situation," she told CTV's Canada AM.

"He wanted to be a good person and a good Jew, and that's why he chose to go and live in Israel and build a family there."

Trompeter said everybody who knows Rotman is thinking of him and his family.

"It's a tough time for everybody who knows Howie, and for Jews around the world, just in the context of the larger horrific attack," she said. "It was a massacre."

Trompeter had previously lived in Har Nof, the west Jerusalem neighbourhood where the attack took place. She said that neighbourhood residents are still in shock.

"Until now, I think everybody felt it was very safe. And now, I think people are in shock and just pondering what's going to happen in the future," she said. "It's a small community and everybody knows somebody that in some way was involved."