Initial tests indicate that Charles has torn his anterior cruciate ligament and will miss the rest of the season, a team source told NFL Network insider Jason La Canfora. The Chiefs will learn Charles' final diagnosis after an MRI exam scheduled to be performed Monday morning.
Charles, who rushed for 1,467 yards last season, was lunging toward the first-down mark along the Lions' sideline when he was pushed out of bounds by defensive back Chris Houston. Charles landed at the feet of Detroit's mascot and immediately began clutching his left leg.
It appeared Charles might have hurt himself while planting the leg as he went out of bounds -- he seemed unwilling or unable to plant it again as he fell to the ground. Charles also appeared unable to put any weight on his left leg as he was helped onto the cart.
Charles, 24, has rushed for over 1,100 yards in each of the last two seasons, and his injury was the latest bit of bad news for Kansas City. The Chiefs, who won the AFC West last season, were routed 41-7 by the Buffalo Bills in their opener and trailed the Lions 20-3 at halftime.
The Associated Press contributed to this report.