Paula Radcliffe has declared the International Olympic Committee's refusal to implement a blanket ban on Russia from the Rio Games as a "sad day for clean sport".
The IOC announced on Sunday it would instead be the responsibility of each sporting federation to check the doping records of Russian competitors under its jurisdiction.
The decision, announced after a three-hour meeting via teleconference of the IOC's executive board, comes just 12 days before the opening of the Games on August 5.
The governing body has been under huge pressure to throw Russia out of the Games after a second World Anti-Doping Agency-funded investigation found proof of a doping programme directed by the Russian state.
And Radcliffe - who competed at four Olympics between 1996 and 2008, finishing fourth in the Sydney 2000 marathon - has accused the IOC of failing to adequately deal with the ongoing crisis.
A statement published on the 42-year-old's Twitter account read: "A sad day for clean sport.
"A decision that shows that the IOC's primary concern is not to protect the clean athletes, not to be able to look them in the eye and promise they did all they could to ensure a level playing field.
"While it throws a political lifeline to Russia that surely came with promises and assurances, it is unfair to leave it up to federations at such short notice, particularly the smaller federations who will lack the resources to check the criteria."
Russia's track and field athletes have already been banned by the IAAF and other federations now face a race against time to establish those Russians who meet the criteria set out to allow them to compete in Brazil.
Russians who have already served a suspension for doping - such as swimmer Yulina Efimova - have also been banned but athletes from other countries with prior indiscretions will be allowed to compete in Brazil.
Radcliffe said: "While I applaud no athlete going to the Games who has previously served a doping suspension - this cannot fairly be only Russian athletes.
"A truly strong message for clean sport would have been to ban all those who have been caught cheating. In short, it does not send the clear message it could have done that doping and cheating in all Olympic sport will never be tolerated."
Fellow long-distance runner Jo Pavey also admits she has been left "disappointed" by the IOC ruling.
The 42-year-old posted on her Twitter account: "Such a disappointing decision by the IOC. Does not send out a strong message that doping will not be tolerated."
Javelin thrower Goldie Sayers was also frustrated. She wrote on Twitter on Sunday: "The IOC have missed the biggest moment in their history to honour the dedication & sacrifice clean athletes make to compete at the Olympics"
Olympic gold medal-winning rower Mark Hunter told BBC Radio 5 Live: "I'm sickened by it, it was a chance for the IOC to really stand up and make a stand.
"I'm just really disappointed. You are going to have Russian athletes sitting on the start knowing that people are sitting beside them that aren't really trusting or believing them."
Two-time gold medallist James Cracknell says the IOC "bottled it". The rower added on his Twitter account: "IOC passing the buck to individual federations on whether to allow Russian athletes to compete in Rio 2016. Bad day."
WADA had recommended for all Russian athletes to be banned after a report led by Canadian lawyer Richard McLaren revealed evidence of widespread state-sponsored doping by the country during the 2014 Sochi Winter Olympics.
Despite the IOC saying it would not accept the entry of any Russian athlete that could not meet a list of conditions, sports minister Tracey Crouch was left underwhelmed by the IOC's decision.
In a statement, she said: "While this is solely a decision for the International Olympic Committee, the scale of the evidence in the McLaren report arguably pointed to the need for stronger sanctions rather than leaving it to the international federations at this late stage."