According to a report in Dutch newspaper De Telegraaf, Americans George Hincapie (BMC), Levi Leipheimer (Omega Pharma), Christian Vande Velde and David Zabriskie (both Garmin) have confessed to doping.
The report added that they testified against Armstrong and would receive bans of six months beginning at the end of the season.
The New York Times later Thursday reported the same four riders would testify against Armstrong, citing two unnamed sources close to the investigation.
All four riders are currently taking part in the Tour de France, and are said to have given evidence in the US Anti-Doping Agency (USADA) investigation which has charged former US Postal team leader Armstrong with doping.
Jonathan Vaughters, another former US Postal rider who is now CEO of Garmin, is also at the Tour but denied the claims in the report.
Hincapie, a teammate of Australian Tour de France champion Cadel Evans, refused to directly comment on the report ahead of Thursday's fifth stage from Rouen to Saint-Quentin.
"I'm just disappointed this is being brought up once again," said Hincapie, the only rider to accompany Armstrong in all seven of his triumphant Tour campaigns.
"I've always tried to do the right thing for the sport. Right now I'm here to do my job and I'm going to try and focus on that.
"BMC's got nothing to do with this, Cadel is obviously here to try and win the Tour and I'm going to try and help him do that."
Asked if he had spoken to Armstrong, Hincapie added: "I haven't in a while. I'm sad he's going through this. He's done so many things for the sport. His accomplishments are incredible."
The BMC team said earlier they had received no notification concerning an eventual suspension of Hincapie.
"I can tell you we have not received any notification from any authority about this issue at all. So therefore we have no comment," said BMC team manager Jim Ochowicz.
Ochowicz is the former manager of Motorola, the team Armstrong belonged to before he contracted cancer in 1996. It was after Armstrong's return to the sport in 1998 that he joined US Postal.
Ochowicz added: "First of all we don't give comments about media stories that are written and we have no information about. George is here to race the Tour de France."
Garmin owner Vaughters immediately issued a denial on his Twitter account.
"Regarding the Dutch media report: No 6mos suspensions have been given to any member of Slipstream Sports. Today or at any future date," wrote Vaughters, whom De Telegraaf claimed had also admitted doping.
Leipheimer meanwhile refused to comment when asked if he had testified against Armstrong.
"I'm here to race the Tour de France and I've got nothing to say about the report," he said.
"I don't think it would help the situation, the speculation, so I'm not going to say anything about this report. I'm 100 percent committed to doing my best race."
USADA has said previously that at least 10 former Armstrong teammates and associates would testify against him, but vowed to keep the names confidential.
"No individual cases have been finalized and any attempt to guess at whom potential witnesses might be only leads to inaccurate information being reported and subjects those named to unnecessary scrutiny, threats and intimidation," USADA chief executive Travis T. Tygart said in a statement.
"It is important to remember that the truth would often be suppressed without witnesses who at great cost to themselves are willing to tell the truth under oath about what they saw and experienced, and any attempt to circumvent the proper procedures in order to bully or silence people who may or may not be witnesses cannot be tolerated."
A three-member independent anti-doping review board has found sufficient evidence to push forward with formal charges and a hearing against Armstrong.
Armstrong, 40, has always insisted he is innocent, saying he has passed more than 500 drugs tests.
Reacting to this latest twist he wrote on his Twitter page: "This isn't about @usantidoping wanting to clean up cycling - rather it's just plain ol' selective prosecution that reeks of vendetta."