McDonald was injured on the final play of the Blues' 2-1 overtime loss to Edmonton on Saturday night.
Blues coach Davis Payne said McDonald is day to day, but declined to reveal if the center sustained a concussion when he was hit in the head by the knee of Oilers forward Shawn Horcoff. Taylor Hall scored the winning goal on a breakaway created by the collision that left McDonald down on the ice.
"We re dealing with the upper body right now, and until we get home and get the evaluations done that will be as much information as we have," Payne said about 90 minutes before the Blues faced the Canucks.
McDonald flew with the team to Vancouver on Saturday night and is expected to return to St. Louis on Monday.
The Blues, who brought a five-game losing streak into Sunday's game, were already playing without top-scoring forwards T.J. Oshie and David Perron. Oshie broke an ankle on Nov. 10. Perron sustained a concussion six days earlier.
"It should familiar territory for us," Payne said. "It's just another situation where we have to band together and be very good as a group."