The owner's wife, who did not want to be named, told the Herald on Sunday that the incident occurred when her husband and her mother-in-law tried to apprehend a woman.
The liquor store owner told the Herald on Sunday there had been an incident earlier in the night at the store.
The group had returned later and there as a yelling match leading up to the incident.
About an hour after the incident he said his mother was "not doing very good".
Detective Mike Flatt said police were speaking to two people in relation to the assault.
"CIB are involved as well, we are following through with a female and male who were involved," detective Mike Flatt said.
"They were in the vicinity and independent witnesses pointed them out so they are back here assisting us with our inquiry."
Flatt said there was CCTV footage that had been viewed by officers.
Police had been informed of an earlier incident at the store and Flatt said they were on their way to the store to investigate when they got the call to say the woman had been seriously injured.