The Toronto defenceman suffered a concussion and back spasms from the ugly hit he took from Janssen in Friday night's game. Kaberle, the Leafs' top blue-liner, is out indefinitely.
"We don't know how long (Kaberle will be out)," Leafs GM John Ferguson said before Saturday's game against Buffalo. "It's too early to tell."
Janssen, a tough guy with the New Jersey Devils, was suspended for three games by NHL discliplinarian Colin Campbell on Saturday, Campbell feeling the hit was too late.
"There's no correlation between Cam Janssen getting suspended three games and the Toronto Maple Leafs losing a key player like Tomas Kaberle at this time of year, especially after the trade deadline," Ferguson said.
"It's as bad a hit that I've seen in a long, long time."
No penalty was assessed on the play by referees Kelly Sutherland and Brad Watson.
Kaberle, who was conscious and communicative after being taken off the ice on a stretcher, spent the night under observation in hospital.
Kaberle was hit in his own end after passing the puck to Carlo Colaiacovo. The puck was on Colaiacovo's stick when Janssen drilled him in the head with his left shoulder. Kaberle spun head-first into the side boards and appeared to be unconscious as he lay face down on the ice. He was sitting up on the ice when a plastic brace was attached to his neck before he was strapped to the stretcher.