Officers were called to the Co-op in Broadway, Hawksworth, just before 7.25am to reports of an assault.
Police are still establishing the full circumstances, but said a female shop worker had been hit in the face with a bottle.
A spokesman said the victim had been treated by paramedics and taken to hospital.
Her attacker was described as a mixed race man who was aged in his mid 30s.
Back in March, police issued an appeal after armed robbers threatened a woman at knifepoint and assaulted her as she was forced to open the safe.
Anyone with information on the latest incident is asked to call police on 101.