The 63-year-old needed hospital treatment after being attacked by a man in Cleland Newsagents on Neilston Road, Paisley, yesterday.
The robber fled with a two-figure sum of cash and left his victim, a popular figure in the community, extremely distressed.
Police are asking anyone with information about the attack, which happened at around 12.45pm in a busy area, to come forward.
The suspect is described as white, around 5ft 7in and unshaven. He was wearing a black hooded top with the hood up and dark trousers and was carrying a black rucksack with a white motif on it.
Officers are gathering and reviewing CCTV images from the area to get more details about the suspect.
The woman has now been released from the Royal Alexandra Hospital, where she had been receiving treatment.
Detective Sergeant Peter Crombie, of Police Scotland, said: "This has been a particularly violent assault leaving an elderly woman seriously injured and extremely distressed. She has worked in the shop for 26 years and is well known and popular with local people.
"I'm sure someone in the community has information about the suspect or the incident and I urge them to get in touch with us - please don't protect a man who is capable of committing such a vile, unprovoked attack on an elderly woman.
"This incident happened in the middle of the day in a busy area with a pub and garage nearby, did you see this man, did you notice anything odd, please get in touch with us, any information, no matter how insignificant it seems to you, could prove vital in our investigation and help trace the man responsible."
Anyone with information is asked to contact officers in Paisley on 101.