The 29-year-old centre, who has an upper-body injury, didn’t take the ice for the morning skate and later was ruled out of the contest by Blues head coach Ken Hitchcock.
“He’s our number one centre … he plays in every situation,” Hitchcock, whose team is ahead 2-0 in the best-of-seven series, told reporters. “Somebody’s going to have to do extra work killing penalties … we’re going to have to do a better job on faceoffs.
“What would Chicago be like with losing [centre Jonathan] Toews? For us, Backes is Toews.”
Backes was forced from Game 2 Saturday at 15:09 of the third period when Blackhawks defenceman Brent Seabrook checked him to the head on a late hit into the end boards, according to the NHL’s department of player safety.
Seabrook, was assessed a five-minute charging penalty, was suspended three games on Sunday. He will be eligible to return April 27 for Game 6, if necessary.
Blues rearguard Kevin Shattenkirk said his team must take advantage of a weakened Chicago blue-line.
“We all have to lead each other,” he told reporters. “It really just comes from playing the right way, keeping our emotions in check and playing a really solid team game.”
St. Louis will have forwards Patrik Berglund (upper body) and Brenden Morrow (foot) back in the lineup.
“It’s a big hole [filling Backes’s spot] but I think we’re more equipped with Berglund in our lineup,” Hitchcock said. “We’re more equipped to handle this than we would have been without ‘Bergie’ here.”
Berglund has practised three times in the past four days.
Morrow, who didn’t play Saturday, had been nursing a foot injury suffered April 10.