Seabrook was assessed a major penalty and game misconduct for the incident, which happened in the third period of the Blues 4-3 win over the Blackhawks in Game Two of their first round Stanley Cup playoff series.
Seabrook, who had never been suspended or fined in 11 NHL seasons, drove his shoulder into Backes' head leaving him dazed on the ice.
Backes had to be helped to bench and did not return to the game. It is not yet known how long he will be out of the St. Louis lineup.
The loss of Seabrook is also a major blow to the Stanley Cup champion Blackhawks, who trail the best-of-seven series 2-0.
(Reporting By Andrew Both in Cary, North Carolina. Editing by Steve Keating.)