The Jockey Club confirmed on Thursday it is withholding prize-money for the Group II race while it continues to establish whether the sample contains traces of a prohibited substance in breach of its rules.
If the 'A' sample is deemed positive, a second 'B' sample taken at the same time after the race would be sent for analysis before the test results are confirmed, but the procedure has yet to reach this stage.
Jockey Club PR director John Maxse told Racing Post: "The current situation is that Gerard Butler has been sent a letter, which informs him that the test has not been cleared, and that the prize money for the Richmond Stakes will remain on hold for the time being.
"The testing process is ongoing. As yet no B sample has been sent away for confirmatory analysis so at this stage it would be premature to assume what the outcome will be.
"There is concern about a sample and we are awaiting further direction from the laboratory."
Elusive City, who extended his unbeaten record on Sunday with a win in the Prix Morny that has put him among the favorites for next year's Sagitta 2,000 Guineas, has been treated for stomach ulcers.