The international sports tribunal raced Monday to decide appeals by Russian athletes against their ban from the Rio Olympics with the opening ceremony just four days away.

The restricted opening of a new metro line for the Olympic zone also highlighted the struggle cash-strapped Rio organisers have faced to get Games stadiums and facilities ready and cleaned up on time.

Swimmer Yulia Efimova and wrestler Viktor Lebidev registered appeals at the Court of Arbitration for Sport (CAS) taking the total number of Russian challenges to International Olympic Committee sanctions to four, with more possible.

Cases involving swimmers Vladimir Morozov and Nikita Lobintsev, who won medals at the 2008 Beijing and 2012 London Games, were to be completed on Monday when the hearing of Efimova, who took bronze in the 200m breaststroke in London, was to start.

Seven Russian swimmers were banned from Rio by FINA after the IOC ordered sporting federations to exclude any Russian competitors implicated in an investigation into Russia's doping scandals by Canadian lawyer Richard McLaren.

McLaren's report for the World Anti-Doping Agency (WADA) said there was a state-organised doping scheme in Russia, with the secret service helping the sports ministry to manipulate samples.

At least 117 of the 387 competitors Russia had wanted to send to Rio have been excluded.

In parallel there have been recriminations over who is to blame for the huge doping controversy revealed in a German television documentary in 2014 and now casting a shadow over the Rio Games.

IOC president Thomas Bach rejected suggestions at a press conference that the chaos represented a "huge failure" for the IOC.

"The IOC is not responsible for the timing of the McLaren report," he said in a veiled attack on WADA.

"The IOC is not responsible for the fact that different information which was offered to WADA already a couple of years ago was not followed up."

Russian anti-doping agency whistleblower Vitaly Stepanov says he first began passing information to WADA in 2010.

WADA has said it did not have the power to act on the information and insisted that its priority was to protect Stepanov and his wife Yulia Stepanova, who are now in hiding in the United States.

Bach said the IOC was not responsible for the accreditation or supervision of anti-doping laboratories in Russia.

"So therefore the IOC cannot be made responsible neither for the timing nor for the reasons of these incidents we have to face now and which we are addressing and have to address just a couple of days before the Olympic Games," Bach said.

But he insisted the doping scandal would not taint Rio.

"I don't think this event will be damaging. I trust people will realise the difficult situation we are in. We did our best to address the situation in a way to protect clean athletes."

Three IOC executive members have been named to make a final decision on which Russian athletes will compete in Rio once the individual federations have made their lists.

The IOC said the Russian team will be finalised before Friday's opening ceremony at the Rio Olympic stadium.

The Rio Games has also faced criticism over the state of the athletes' village and the readiness of venues.

Bach said that on his arrival Thursday, he had gone straight to the athletes village "unshaven" to see the conditions where hundreds of plumbers have been working on water pipes following complaints from some teams.

He said athletes are now happy.