Decker got tangled up with Finnish defender Ronja Savolainen and was in audible distress on the ice.
Medical personnel rushed to her aid and Decker was stretchered off the ice. She didn't return.
Decker, 30, has played in three Olympics including the Americans' golden triumph in 2018.
She's the author of the first hat trick in National Women's Hockey League history and a six-time gold medalist at the World Championships.