Officers responded after receiving a report that two unknown men entered the mini market on Robin Lane, Beighton, just before 8am, this morning, Sunday, February 16.
A South Yorkshire Police spokesman said one of the suspects is understood to have assaulted a member of staff who was taken to hospital with suspected stab wounds.
The other suspect is believed to have taken items from the shop before both men fled the scene in the direction of the Fox Inn.
Police cordoned off an area near the shop and the junction with Victoria Road as part of their on-going investigation during the day.
Enquiries are ongoing and anyone with information is asked to call police on 101 quoting incident number 198 of February 16.