It happened around 10pm at the Smashburger on Eldridge Parkway near Briar Forest.
Police say the suspect simply walked up and threatened the employees inside. The manager rushed them to the kitchen. That's when the suspect pulled out a shotgun and shot a lock on the door. The lock hit the manager in the chest, but he was not seriously hurt.
The suspect fled the scene without any money.
Police say a robbery at a second Smashburger happened about 15 minutes later on South Main near Kirby in southwest Houston.
Authorities say they believe the robberies are connected but that a second suspect was involved in the second robbery. No one was injured.
Investigators say they believe a group of suspects is targeting Smashburger restaurants.