The National Anti-Doping Agency (NADA) said that women's 4x400m relay runners Mandeep Kaur and Sini Jose tested positive for banned steroids and were suspended pending the results of their B samples, which are due in the coming days.
NADA director-general Rahul Bhatnagar told AFP that the findings - among six positive tests for steroids on Indian athletes in recent days - made it unlikely that either would compete in the British capital.
"Because they've reached national level, they've been tested hundreds of times. It's not that they're not aware (of banned drugs)," he said.
"With steroids I'm doubtful if they would get a reprieve. If they're banned for two years, they won't get a chance to compete in the Olympics."
Hopes have been high in India for its women's 4x400m relay team since they won the country's first-ever Commonwealth Games track gold in front of home fans in New Delhi last October.
They repeated their success in November at the Asian Games in Guangzhou, China. Kaur and Jose were part of both winning teams.
India has never won a track medal at the Olympics.
The closest the country came was in Los Angeles in 1984, when P.T. Usha narrowly missed a bronze in the women's 400m hurdles and in Rome in 1960, when Milkha Singh was edged into fourth in a photo-finish in the men's 400m.
NADA's Bhatnagar said two other female 400m runners, Tiana Mary Thomas and Jauna Murmu, plus a female shot-putter, Sonia, also tested positive.
The Times of India newspaper on Friday said all four one-lap specialists were trained by the same Ukrainian coach.
"It's the samples of the athletes that's tested positive," said Bhatnagar. "There's no evidence that the coach had a role but if we get information that the coach was involved in this then the coach can also be suspended."
Kaur, Jose, Thomas and shot-putter Sonia tested positive after a national track meet in the southern city of Bangalore late last month.
Murmu and leading Indian male long-jumper Hari Krishnan Muralidharan, who also gave positive samples, were tested out of competition.
India's anti-doping agency regularly conducts sessions with Indian athletes to inform them about banned substances, including those in medicines.
But doping has afflicted Indian sport over the last decade, with weightlifters being the chief culprits.
Seven Indian athletes - four wrestlers, a shot-putter and two swimmers -- were suspended for taking the banned stimulant methylhexaneamine in the run-up to the last Commonwealth Games.
The suspensions were lifted after the World Anti-Doping Agency (WADA) re-classified the stimulant, which is widely used as a nasal decongestant, allowing them to compete.
Four other Indian athletes who were not picked for the Games but also failed tests were also reprieved.
During the Games, an Indian athlete competing in the women's 20km walk tested positive for the banned substance nandrolone, while in June this year, an Indian footballer was banned for two years for failing a dope test.
India's cricketers were also embroiled in a row in 2009 for failing to sign up to a global drugs code, claiming that a WADA clause requiring them to state their whereabouts for testing infringed their privacy.
Doping menace hits Indian Olympic track medal hopes
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