An altercation in a Detroit branch of Burger King has led to a member of staff striking a 67-year-old customer.
The man, who reportedly had been causing a disturbance at the restaurant, fell and later died.
The punch may have caused him to choke on his dentures, local TV station WJBK-TV reported.
An autopsy to establish the cause of death is expected to take place on Friday. Officials say the employee could face criminal charges.
Sgt Eren Stephens, of the City of Detroit Police Department, told reporters: "A verbal argument occurred. It escalated into a physical altercation."
Burger King spokeswoman Denise Wilson said that company officials were aware of the incident, and that the franchise owner was co-operating with police.