By Karolos Grohmann

(Reuters) - The leaking of a draft letter urging a complete ban on Russian athletes at the Rio de Janeiro Olympics has undermined a key report into doping allegations at the 2014 Sochi Games, WADA board member Nenad Lalovic said on Sunday.

The leaked letter, addressed to the International Olympic Committee (IOC), backed by several anti-doping agencies and circulated to the World Anti-Doping Agency's (WADA) athlete committee, called for all Russian athletes to be banned from the Rio Games.

Russia's track and field athletes are already banned from competing in Rio by the world governing International Association of Athletics' Federations (IAAF) over widespread doping in the sport.

The letter was due to be sent once a report into allegations of state-backed doping at the Sochi winter Olympics led by Canadian law professor Richard McLaren is presented on Monday.

Lalovic, who heads United World Wrestling and is also a member of WADA's foundation board, said the letter would weaken the McLaren report, if it offered clear evidence of doping offences.

"Unfortunately this report is harmed by all the events before the report is public," Lalovic told Reuters. "Obviously the report focuses on the situation in Russia but we cannot generalize so easily. Of course it has been harmed now.

"Nobody will now take it as seriously as it should be because it seems that a lot was known in advance."

The letter, obtained by Reuters on Saturday, was drafted by United States Anti-Doping Agency (USADA) CEO Travis Tygart and his Canadian counterpart Paul Melia.

It has the support of several other anti-doping bodies including Germany, New Zealand and Japan, as well as some athletes groups, according to Tygart and Melia.

It was also circulated to WADA's Athlete Committee members by Canada's Beckie Scott, who chairs the committee, asking whether they would support it.

Lalovic said he had not received a copy of the letter despite being on WADA's decision-making body.

"If we have drafts of letters being circulated asking to ban all Russian athletes then that is strange," Lalovic, who is also an IOC member said.

"USADA should be focused on the health of American athletes and those competing in the United States. Now it seems that USADA and the Canadians took over responsibility of WADA. Nobody entitled them to do that."

(Reporting by Karolos Grohmann; Editing by Toby Davis)