Detectives today released details of the attempted robbery at Sainsbury's in Chapeltown Road, Pudsey.
It happened at around 10.50pm on Friday when three masked men entered through an open fire door at the back of the building as staff were preparing to close up for the night.
A police spokesman said: "A male member of staff was hit on the head with a weapon causing an injury, before the men threatened his female colleague with a knife.
"They demanded the safe be opened but the staff did not have access.
"The men then left the store empty-handed and were heard to drive off at speed."
The male member of staff who was injured was treated at hospital but his injuries were not serious, police said.
Anyone who witnessed the incident or who has any information is asked to contact Leeds District CID via 101, quoting crime number 13180019969.
Alternatively, call the independent charity Crimestoppers anonymously on 0800 555 111.