Chargers wide receiver Keenan Allen has been carted off the field late in the second quarter of their game against the Chiefs with what appears to be a serious right knee injury.

Allen was making a cut toward the sideline on a passing route when he went down. He ripped off his helmet as trainers began tending to him, and was helped into the back of a cart and taken off the field.

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There was no immediate word on the extent of the injury.

Allen, who missed the last eight games a year ago with a lacerated kidney, had six catches for 63 yards before he was hurt. The Chargers led 21-3.