Former Olympic 100 metre champion Justin Gatlin hopes to have his four-year ban from competition reduced to no more than two years when he takes his case to the Court of Arbitration for Sport tomorrow.
Gatlin tested positive for excessive levels of testosterone at the Kansas Relays in 2006.
He was given an eight-year ban by the International Association of Athletics - reduced to four years on appeal by the American Arbitration Association in January - as it counted as his second doping offence.
The first offence came in 2001, when Gatlin tested positive for amphetamines.
A two-year ban issued for that offence was lifted after Gatlin served 13 months. The reduced sentence followed a ruling that the first positive test was a result of prescribed medication for Attention Deficit Disorder, taken while Gatlin was a student at the University of Tennessee.
Gatlin wants the 2006 test treated as a first offence, which would carry a maximum ban of two years - time he has already served.
If a two-year ban were imposed for the 2006 test, Gatlin would become eligible in May, allowing him to compete in Olympic trials in June.
Gatlin also has claimed that his positive test at the Kansas relays was the result of sabotage and has pointed to his role as an anti-doping spokesman as recently as 2005.
However, the IAAF is strongly opposed to the appeal, filing an appeal of its own to the CAS in January to request a lifetime ban for Gatlin - the normal punishment for two failed doping tests.