Harris County Sheriff's Office deputies were called to a strip mall in the 13000 block of Veterans Memorial near F.M. 1960 around noon Saturday for the shooting.
Officials said least two people were taken into custody and the victim was rushed to Ben Taub General Hospital.
Witnesses on the scene said he was shot in the upper leg area.
The victim's name has not been released, but we are told he is a man in his 60s who seemed to be in the wrong place at the wrong time.
Customers lined the shopping center in shock as deputies handcuffed two men outside the El Ranchito Meat Market.
"One of the suspects went up to the sales counter and was robbing the clerk there while the second suspect went up to a check cashing window inside the business," HCSO Sgt. Robert Tonry said.
Deputies say the two men stormed in with guns drawn. Their faces were covered by bandanas.
When one customer stepped in between a suspect and clerk at the cashier booth, the suspect's gun fired, striking another bystander.
"Unknown what his condition is, but I believe it's not life-threatening," Tonry said.
The suspects hopped into a black pickup truck and tried to flee, rushing past Victor Burke, a vendor outside El Ranchito. He said they were only inside for two to three minutes and ran off carrying guns and two bags.
"He got two bags. One bag, one guy, another bag, the other guy," Burke said.
Eyewitnesses from the scene followed the suspects and called police. Authorities brought the pair back to the store where they were detained.
The same customers who saw them rush off reunited with them to confirm their identities for law enforcement.
Charges against the suspects are pending.