The worker at Asda in Old Horns Crescent, Great Barr, was assaulted at around 6am this morning.
Police are now appealing for anyone with information to come forward.
A spokeswoman for West Midlands Police said: "Police are investigating an assault at Asda in Old Horns Crescent, Great Barr, Birmingham which took place just before 6am this morning.
"It’s alleged that three people were involved in an altercation with a security guard who was hit in the face, causing a minor injury."
Anyone with information is asked to contact police via Live Chat at west-midlands.police.uk between 8am and midnight or call 101 anytime. Crimestoppers can be called anonymously on 0800 555 111. Quote crime reference 20BW/30908K/19.