The IOPC investigation has been in the closing stages for several months, ahead of a planned inquest later this year.
Mr Atkinson, aged 48, died after being shot with a Taser by police outside his father’s house in Meadow Close, Trench, on August 15, 2016.
The investigation into Mr Atkinson’s death was delayed by a scandal involving a private forensic testing company.
Mark Pearson, of the IOPC, said: "The pathologist recommended a report from a further medical expert which has been completed, and is being considered by the pathologist in finalising their report.
"We are keeping Mr Atkinson’s family, West Mercia Police and HM Coroner regularly updated.”
Atkinson was one of the best known and well-loved players of his generation, scoring a hat-full of goals for Villa under Ron Atkinson.
He won a League Cup during his time at the club.
Cheryl Hooper investigation
Meanwhile, a separate investigation into two police forces over the handling of complaints by a Newport woman who was later shot and killed outside her home is also ongoing.
West Mercia Police and Staffordshire Police is being investigated over Newport woman Cheryl Hooper, who reported incidents to both forces before she was killed in January.
She died from a gunshot wound to her neck outside her home on January 26.
The investigation comes after both police forces referred themselves to the IOPC.