DETROIT -- Kansas City running back Jamaal Charles will likely miss the rest of the 2011 season after an initial diagnosis revealed a torn ACL in his left knee following the Chiefs' 48-3 loss Sunday, a source familiar with the situation told ESPN NFL Insider Adam Schefter.

The source said Charles will have an MRI on Monday to confirm the diagnosis, but the team believes the Pro Bowl running back will not return this year.

Coach Todd Haley said after the game the team was still awaiting a definitive word on his status.

"We'll probably know a lot more on him here in the next 12 hours or so," Haley said.

Charles, who rushed for 1,467 yards last season, was lunging toward the first down mark along the Detroit sideline when he was pushed out of bounds by defensive back Chris Houston. He landed at the feet of Detroit's mascot and immediately began clutching his left leg.

His return was initially announced as questionable, but the injury appeared significant, and he was carted off the field. Charles was declared out for the rest of the game early in the third quarter.

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.

The 24-year-old Charles has rushed for over 1,100 yards each of the last two seasons, and his injury was the latest bit of bad news already for Kansas City this season. The Chiefs, who won the AFC West last season, were routed in both of their games this season and have the worst two-game point differential of any defending division champion in NFL history.

Todd Haley said the team expects more information on Jamaal Charles' injury Monday, but the prognosis doesn't look good. Tim Fuller/US Presswire

In the opener against Buffalo, the Chiefs lost Pro Bowl defensive back Eric Berry to a season-ending injury -- also to the left knee and also in the first quarter.

"The season will not be canceled as far as I know," Haley said of the injuries. "What we have to do is we have to stop doing those things that are costing us dearly, and putting us in very difficult positions."

Even with Charles sidelined, the Chiefs rushed for 151 yards in the game. Thomas Jones had 40 on a team-high 12 carries.

Jones actually had more carries than Charles last season and rushed for 896 yards.

Information from The Associated Press contributed to this report.