Hamilton police Constable Hayden Puke said three of the offenders tried to get into the shop through the back door while the other approached Farrar with a knife and demanded money.
"The shopkeeper has tried to defend himself and as a result sustained significant injuries to his eye, face and hands.
"The masked offenders then fled the store, running south on Irvine St."
Police would also like to speak to the people in the attached imagery as they "may be able to assist with inquiries".
Anyone with information that could assist with inquiries is asked to please contact Constable Hayden Puke on 07 858 6200.