Thomas did not play in the final five minutes of regulation, nor did he take a shift in overtime during Saturday's comeback win.
Blues Head Coach Craig Berube said Thomas is considered day-to-day.
"It's a huge loss for sure," Berube said. "For a guy who probably has the most puck possession on the team every night, has the puck a lot, does good things with it, guys are going to have to dig in and help out. But we've got enough guys to handle it and get the job done."
Thomas has played in 21 games for the Blues this season and leads the team with 19 points (four goals, 15 assists).
