"He broke C5," Avalanche coach Jared Bednar said Sunday following the results of a CT scan. "He has a fracture."
Cogliano, 35, is scheduled to undergo a follow-up MRI exam.
He suffered the injury during Game 6 against the Kraken when he was hit into the boards from behind by Seattle forward Jordan Eberle. Cogliano went to the locker room as Eberle served a penalty for boarding. Cogliano later returned to the game, which Colorado won 4-1 to tie the first-round series at 3-3. Game 7 is Sunday night.
Eberle was not disciplined further by the NHL.
"I don't like the hit," Bednar said. "From 5 years old, you're wearing stop signs on your back on every jersey."
Cogliano was an instrumental player in the franchise's third Stanley Cup championship last season. He brings grit, tenacity and experience to the ice for the banged-up Avalanche. His 120 career playoff games are the most of any current Avalanche player.
Colorado is already without captain Gabriel Landeskog, who has been sidelined all season after knee surgery. The Avalanche are also missing Valeri Nichushkin for personal reasons. Nichushkin has not played since Game 2 on April 20, when he scored in Colorado's 3-2 victory.
Cogliano recorded 19 points (10 goals, nine assists) in 79 games in the regular season. He has 445 points (184 goals, 261 assists) in 1,219 career games over 16 seasons with five teams.
The Associated Press and Reuters contributed to this report.