St. Louis, however, will have centre Patrik Berglund for Monday night's game against the Stanley Cup champions, who trail the playoff series 2-0. Berglund missed three games, also with an upper-body injury.
Backes was wiped out by a big hit from Blackhawks defenceman Bren Seabrook in the third period of St. Louis' 4-3 overtime victory Saturday. The captain was helped off the ice and did not return.
Seabrook received a five-minute major and game misconduct penalty. He then was suspended for three games by the NHL.
Berglund was injured in the third period of St. Louis' 3-0 loss at Dallas on April 12. Berglund had 14 goals and 18 assists this season.