Winona Costin will miss the first Group One meeting of the Sydney autumn carnival after she failed to gain a medical clearance to ride.

The apprentice was ruled out of the midweek meeting at Rosehill and Thursday's provincial program at Hawkesbury after she failed a concussion test following a serious race fall at Canberra on Sunday.

She had hoped to be cleared to ride at Randwick on Saturday but was ruled unfit by a Racing NSW doctor.

Costin had been booked for six mounts including Centre Pivot in the Chipping Norton Stakes.

She will undergo another medical assessment on Monday when she hopes to be given the green light to return to race riding.