According to Sportsnet 650's Brendan Batchelor, Keeper was screaming in pain on the ice before staff helped him onto the stretcher.
Head coach Travis Green didn't have an update on Keeper's condition after the practice.
"It's unfortunate for sure," Green said. "I thought his game had gotten better as camp has gone on these three days. You never like to see anyone laying down on the ice and get carried off in that way."
Keeper, 25, signed a two-year contract with the Canucks in free agency after spending the past three seasons in the Florida Panthers organization. He has appeared in two NHL games in his career and 72 AHL games over the past two seasons.