Brewer will be sidelined indefinitely, but coach Andy Murray expects the 29-year-old defenseman to be back on the ice sometime this season.
"We don't have an exact time frame," Murray said. "He's certainly one of our best players. There's nothing we can do about it. He's injured and we move on, same as we have with all the other guys."
Brewer, who has one goal and five assists, is in the second season of a four-year, $17 million contract. He's played in 28 games for the Blues, averaging about 25 minutes per game.
He joins forwards Paul Kariya (hip), Andy McDonald (fractured ankle), T.J. Oshie (high ankle sprain), D.J. King (dislocated shoulder) and defensemen Erik Johnson (torn ACL/MCL in knee) and Jay McKee (fractured finger) on the sideline. Goalie Manny Legace (mild concussion) was taken off injured reserve Friday.
Brewer experienced discomfort in his back last week while the Blues were on a three-game trip. He played at Anaheim and Los Angeles before sitting out at San Jose last Saturday.
"I went from thinking I might not play in San Jose to not moving too good, to my right leg doesn't work properly," Brewer said Thursday. "I'm told every case is different. We'll see where it takes me."
Surgery was his only option, according to doctors who repaired the sciatic nerve.
"The pain was so severe that there had to be a surgical procedure to stop it," Murray said. "It wasn't something that he could even think about playing with."
The Blues (12-16-3) are on a five-game losing streak. They play Minnesota on Saturday.