It happened around 12:30 a.m. in the 5800 block of Westheimer at Fountainview.
Someone drove up in the parking lot and fired several shots, Houston police said.
Investigators were looking into whether an earlier fight at the business was related to the shooting.
Officers arrived to find someone with a gun in their hand in the parking lot, but later determined that the person was not the shooter and was holding the gun for protection.
It wasn't clear if that person had anything to do with what happened.
The gunshots sent people inside the lounge into a panic. At least one customer fled to safety inside a freezer in the business.
The victim's condition wasn't known Sunday.