It happened at Kashmir Meat & Poultry on Wednesbury Road, Pleck, when the suspect walked in and threw the weapon.
The bottle left the man bruised, while the shop was left badly fire damaged. Today, workers were at the scene restoring the electricity supply to the building.
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Zalika Bib, whose husband Bashir Hussain had a lit bottle thrown at him but suffered only bruising, was phoned by him in the immediate aftermath of the attack at 5.20pm.
She told the Express & Star: "I was saying: 'Are you joking?' and he said: 'No, I'm not joking.'
"It makes us feel awful. We're not the type of people to make comments or anything like that," she added.
On whether the business had suffered any antisocial behaviour previously, she said: "There was only one – when a young boy came in. He was only 15, 16 and he threw a can and we called the police. We have never had anything like this before."
Police say they are keeping an open mind over the motive of the attack, which happened at around 5.25pm yesterday.
Brigg Ford, spokesman for West Midlands Police, said: "We cannot say definitively that it was a racist attack.
"The motive is unclear at this stage."
Detectives were examining CCTV from the area today in the hunt for the suspect, who was white, 6ft tall and wearing a blue jacket.
Police will also be in the community to carry out patrols to reassure people.
Det Insp Greg Evans, from Force CID, said: "The inquiry is at an early stage and I am keeping an open mind as to the motive.
"The man was not seriously injured, but it could have been much more serious. I am appealing for anyone with information or anyone who saw what happened to call police on 101 or the independent charity Crimestoppers anonymously on 0800 555 111."