A key report into doping allegations at the 2014 Sochi Games has been undermined after a draft of a letter was leaked. The letter was backed by several anti-doping agencies and it called for a complete ban of Russian athletes from competing at the Rio Olympics.

The leaked letter was addressed to the International Olympic Committee and circulated to the World Anti-Doping Agency's athlete committee, but what not meant to be sent until after the independent report into allegations of state-backed doping at the Sochi Winter Olympics led by Canadian law professor Richard McLaren is presented on Monday.

Russia's track and field athletes are already banned from competing in Rio by the sports' governing body, the IAAF, over widespread doping. WADA board member Nenad lalovic said the leaked letter could weaken the McLaren report, if it offered clear evidence of doping offences.