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 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 generalise. 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."
Swimming's world body FINA also criticised the leak.
"FINA is concerned by the premature calls from U.S. and Canadian Anti-doping authorities to ban Russia from Rio 2016 Olympic Games several days ahead of the publication of the independent McLaren report," it said in a statement.
"FINA is also concerned that there has been a drive behind the scenes...to get a global coalition .... to support the call for the total ban on Russia. All of this is based on the findings of the McLaren Report which is meant to have been independent and confidential.
"Such breaches of confidentiality and the perception of a breach of independence of the report undermine its credibility."
Read the original article on Eurosport: McLaren report into doping 'weakened by leaked letter', says WADA board member