Charles, the NFL's second leading rusher last season, suffered the injury after taking an awkward step while finishing off a run in the first quarter of Sunday's 48-3 loss to the Detroit Lions. A team source told NFL Network insider Jason La Canfora that initial tests indicated Charles tore the anterior cruciate ligament in his left knee. A person familiar with the injury also confirmed to The Associated Press that the ligament was torn.
Chief concern: Another blowout
Charles had an MRI exam Monday, and Chiefs coach Todd Haley said the running back would join tight end Tony Moeaki and Pro Bowl safety Eric Berry on injured reserve. Moeaki tore his left ACL during Kansas City's preseason finale against the Green Bay Packers, and Berry tore his left ACL during a 41-7 season-opening loss to the Buffalo Bills.
"Injuries are part of the game," Haley said. "Sometimes through preparation, sometimes just through freak happenings, and we've seen a little of each."
The Chiefs are off to one of the worst starts in NFL history, being outscored 89-10 by two teams that combined to win 10 games last season. The miserable start has caused talk radio shows to light up with calls for Haley and general manager Scott Pioli to be fired, even though the franchise is coming off a surprising 10-6 season in which it won the AFC West title.
Haley vowed that the Chiefs would keep working to turn around their season, but that won't be easy after they lost arguably three of their five best players to season-ending injuries.
"It's unfortunate, you know, directly for Jamaal because I know Jamaal had high hopes and was excited and worked very hard to be ready to take this to the next level, and now he won't be able to do that," Haley said. "I know he's hurting pretty good inside. That's first and foremost where my feelings go. But as far as our team, we must step up as a team and move forward."
Wide receiver Jeremy Horne was promoted from the team's practice squad to take Charles' place on the active roster.
The Associated Press contributed to this report.