Britain's most successful female Flat jockey steps in for the Girls team as Gordon is required to ride at Newmarket by Hugo Palmer.
Gordon's agent Philip Shea said: "It's unfortunate, but Hugo gets first call and he needs her to ride in the Sweet Solera Stakes on Saturday."
He added: "It's just a shame that it (Shergar Cup) falls on a day when there are a lot of big Group races.
"Josephine will ride a horse called Jousi in the Sweet Solera.
"She won on her at Ascot last month and she is a lovely filly."
Turner officially retired from the saddle in 2015 but has since made fleeting comebacks, including at the 2016 Shergar Cup meeting.
The 34-year-old also announced on Saturday that she plans to relocate to France during the winter as female jockeys riding across the Channel received a 4.4lb weight allowance in all races.
Turner will be joined in the Shergar Cup Girls team by Melbourne Cup-winning jockey Michelle Payne and Canadian Emma-Jayne Wilson.