The defenseman, who had two assists in 22:57 of ice time in a 5-4 shootout loss to the Vegas Golden Knights on Friday, will be reevaluated in six weeks.
By being placed on long-term injured reserve, Krug will be out a minimum of 24 days and 10 games.
"Obviously a very big part of our team, our back end," Blues defenseman Colton Parayko said. "Tough one, but I think it's just on us to step in. I think we've done a good job of guys coming in throughout the year and just stepping in when needed. Points are crucial obviously for our team and it's just one of those things where we've got to focus on coming to the rink and preparing for each game, no matter who is in the lineup."
Krug has 17 points (five goals, 12 assists) in 31 games this season and is fourth on the Blues in ice time per game (19:37) and blocked shots (43).
"It's a tough break, obviously for him and the team for sure," coach Craig Berube said.
Defenseman
Tyler Tucker
was recalled from Springfield of the American Hockey League on Tuesday. He has 13 points (one goal, 12 assists) in 24 AHL games and has no points in four games with the Blues this season.
St. Louis (16-16-3) lost 5-4 in overtime to the Toronto Maple Leafs on Tuesday, its first game after the three-day holiday break.
NHL.com independent correspondent Lou Korac contributed to this report
