Scotland-born Gallagher, who won track golds at the Beijing and London Paralympics, was tested out-of-competition at a training camp in Italy in July, the Australian Sports Anti-Doping Authority (ASADA) said in a statement on Friday.
"The test was coordinated by ASADA as part of a comprehensive pre-Rio anti-doping program to ensure the integrity of the Australian Paralympic team," ASADA said.
The provisional suspension has ruled 37-year-old Gallagher out of competing at this month's Paralympics in Rio.
The International Paralympic Committee banned Russia's entire delegation from competing at the Paralympics due to state-sponsored doping.
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On Thursday, CAS rejected requests from more than 175 Russian athletes to compete as neutrals.
Last week the Court of Arbitration for Sport (CAS), sport's highest tribunal, rejected a Russian Paralympic Committee (RPC) appeal against the IPC suspension.
Russia appealed against the CAS ruling to the Swiss Federal Court, which declined on Wednesday to issue a preliminary injunction that would have let their disabled athletes compete in Rio.
The court said it would rule later on the team's ban.
(Reporting by Ian Ransom; Editing by Greg Stutchbury)
