Thompson, who suffered the seizure in a special teams meeting, was taken away in an ambulance and hospitalized after the incident and is in stable condition, according to ESPN and the NFL Network.
The 25-year-old defensive end, selected in the fifth round of last year's NFL Draft, played one game and made two tackles for the Chiefs last season, when the club captured a second consecutive Super Bowl title.
The Chiefs, whose medical staff worked on Thompson until an ambulance arrived, called off a scheduled practice session after the medical emergency, with coach Andy Reid and players delaying media interview sessions until Friday.
A mandatory mini-camp for Chiefs players is set to begin on Tuesday.
