The Steelers won't make an official announcement until Mike Tomlin's press conference today, but multiple media sources are reporting that Ben Roethlisberger suffered a Grade 2 MCL sprain of his left knee Sunday in St. Louis.
The normal recovery period for such an injury is two to four weeks, but a bone bruise adds a complication that has set Roethlisberger's recovery range at four to six weeks.
Of course, Roethlisberger has a history of quick healing and general toughness.
He also has a history of missing games against the Baltimore Ravens, the Steelers' opponent on Thursday night.
This week's game will be the sixth Steelers-Ravens game Roethlisberger has missed with either injury or suspension. The Steelers are 1 -4 in those games, all of which were decided by exactly three points.
Roethlisberger was injured Sunday in St. Louis during the Steelers' first possession of the second half. He was hit by safety Mark Barron, who tripped during a blitz and crawled and then lunged into the quarterback's left leg as he was throwing a pass.
Barron wasn't penalized for the illegal hit as Roethlisberger limped off the field and was taken by cart to the locker room.
The initial fear was a season-ending ACL injury, and therefore the MCL sprain and subsequent four-game recovery period can be viewed as a positive finding.
The Steelers' next six games are home against the Ravens, at the San Diego Chargers, home against the Arizona Cardinals, at the Kansas City Chiefs, and home against the Cincinnati Bengals and Oakland Raiders.
Tomlin will discuss the matter further at his noon press conference, and will no doubt name Michael Vick as Roethlisberger's replacement.
Vick replaced Roethlisberger in St. Louis and completed five of six passes for 38 yards.
The Steelers had a 9-3 lead before the injury and finished with a 12-6 win over the Rams to improve to 2-1.