Oshie slid head-first into a goalpost after a push from Dallas' Patrick Eaves during the second period of the same game.
Hitchcock admitted, according to the St. Louis Post-Dispatch, that the play that left Oshie concussed scared him.
Backes exited the ice and underwent an examination in accordance with concussion protocol. Oshie stayed in the game and did not exhibit obvious symptoms.
According to Hitchcock, Oshie's injuries were not limited to his head.
"Oshie has something else going, plus the concussion. We're not sure whether it's the bacterial (infection)," Hitchcock said on Tuesday.
Several Blues players have come down with bacterial infections in recent weeks. Center Jori Lehtera first became ill earlier this month, and forward Joakim Lindstrom missed practice Thursday morning for the same reason. Linstrom is "out right now," said Hitchcock.
Backes has had similar incidents in the last year, including concussion-related symptoms in December 2013 and a head injury after a hit in last season's playoffs.
Paul Stastny is also out of the Blues' lineup with an injury.
St. Louis is 4-3-1 so far this season and is currently fifth in the Western Conference Central Division.
They host the Anaheim Ducks tonight, October 30, at 8 pm EST.