ATHLETICS: Jared Tallent's chances of winning historic back-to-back Olympic gold medals have risen after Italian rival Alex Schwazer failed to have a provisional doping ban lifted.

Schwazer, the man who pipped Australian Tallent for 50km race walk gold at the 2008 Beijing Olympics, missed the London Olympics when banned for testing positive to blood-booster EPO shortly beforehand.

He returned in May and won the 50km event at the world team championships in Rome, beating runner-up Tallent by three and a half minutes.

But the 31-year-old was provisionally banned from competition by the IAAF last month after a May 12 retest of a January 1 sample showed positive traces of steroids.

On Tuesday the Court of Arbitration for Sport (CAS) dismissed a request by Schwazer to lift the ban as the Rio Olympics loom next month, saying it would conduct "an expedited arbitration procedure ... so that a final decision on the merits can be issued as soon as possible".

Tallent will attempt to become the first Australian to win track and field gold medals at successive Olympics when he races in Rio, defending the 50km walk title he belatedly won from London 2012.

The 31-year-old crossed the line second in London but was handed the gold recently after Russian Sergey Kirdyapkin was stripped of the medal for doping.

Schwazer's likely absence in Brazil, along with Russia's athletics ban, greatly improves Tallent's prospects.

If successful he will join Edwin Flack as one of only two male Australians to win two athletic golds.

Flack won the 800m and 1500m at the inaugural 1896 modern Games in Athens.

AAP-AP