Employee came to work high, can we be sued?

An employee came to work high and was very obvious. Impaired speech, red eyes, not able to function. The assistant manager told the manager on duty to step them to the side and talk to them due to concerns of safety and liability. No accusation was done just discussion of if they were okay to work or if they needed a moment. Cannabis is legal in this state but needs to be medical and the employee claims it’s medical. The general manager is mad because they claim the employee could sue over it. Is this the case?