Russian race walker Stanislav Emelyanov has been cleared of doping after a second sample failed to indicate the presence of a banned substance, the IAAF said Wednesday.

Emelyanov, who could be a medal contender at this year's Olympics if Russia's suspension from track and field is lifted, had been facing a lengthy ban for a second career doping offence. But the backup "B" sample did not confirm the original positive finding for EPO.

The IAAF told The Associated Press in an emailed statement that it "has reserved the right to pursue Stanislav Emelyanov for other anti-doping rule violations under IAAF rules" and is seeking legal advice.

In June, Emelyanov tested positive for EPO along with five other Russian walkers at a training centre in the city of Saransk, which has become notorious after more than 30 of its athletes failed doping tests in recent years. A report from a World Anti-Doping Agency commission in November said that staff at the centre had attempted to obstruct drug testers and that Emelyanov had provided an incorrect phone number in a supposed attempt to throw testers off the scent.

It was not clear whether the "other anti-doping rule violations" mentioned by the IAAF were linked to the apparent obstruction. The other five athletes who tested positive along with Emelyanov, including reigning European women's champion Elmira Alembekova, remain under provisional suspension, the IAAF said.

Emelyanov was previously banned in 2014 for doping and was stripped of his gold medal from the 2010 European championships.

He is listed as part of Russia's national team for 2016 on the Russian track federation website. The team list leaves out many athletes who were considered suspicious by November's WADA report, including Olympic gold medal-winning walkers Sergei Kirdyapkin and Olga Kaniskina, whose doping bans ended last month. However, three walkers are included who were present during the alleged obstruction of testers, according to the WADA report.

Notably, the list shows only one runner in the main national team for the women's 800 metres, an event Russia has dominated in recent years. The reigning Olympic champion, Maria Savinova, is among several Russians provisionally suspended after a German TV channel broadcast undercover footage appearing to show Savinova admitting to doping.

Russia's track and field team is not currently eligible to compete at the Olympics after being suspended in November, but the ban could be lifted if the IAAF deems Russia has made progress on reforms.