The plane had taxied to the runway July 30, but the senior pilot was removed before it took off, the Brisbane Courier Mail reported. The female pilot announced the plane had a problem and needed a part.
The Boeing 767-300 returned to the gate and took off about an hour later with a new flight crew.
The pilot, whose identity was not released, was tested for alcohol and was being "withheld from duties on full pay'' while Qantas conducts an investigation, airline officials said.
The Australian air carrier did not disclose the results of the test or indicate when the alleged drinking took place, The Sydney Morning Herald reported. Qantas has a zero-tolerance policy for pilots testing positive for alcohol at any level, the newspaper said.
Passengers said after the plane came back to the terminal, Qantas paid for them to purchase up to $30 each in merchandise.
Of 54,000 pilots, cabin crew and aviation workers tested for alcohol and drugs since 2008, only 45 came back positive, reported the Civil Aviation and Safety Authority, which conducts the tests. No pilots had ever tested positive before.