"The athletes are not suspended now, they are eligible to compete," International Association of Athletics Federations (IAAF) spokesman Nick Davies told a news conference on Thursday.
Davies said an IAAF council meeting on Thursday morning had agreed that its Doping Review Board would start an immediate investigation into the pair after they failed to turn up to a International Olympic Committee (IOC) test on the eve of the Athens Games.
Kenteris, the 2000 Sydney Olympic 200 metres champion, and Thanou, the Olympic 100 silver medallist, later withdrew from the Athens Games.
"The purpose of the inquiry is to establish whether sufficient evidence exists to charge any person with a doping violation," an IAAF statement said. "If such evidence exists, disciplinary proceedings will be instituted."
Davies said if the Doping Review Board found sufficient evidence of a doping violation it would then inform the Greek federation which would conduct its own inquiry. If the two bodies disagree the case would then go to the Court of Arbitration for Sport.
"The process starts immediately. It could take weeks, it could take months but it's a number one priority," Davies said.
"There is a council meeting at the beginning of December. I think it will be concluded by then."
Under IAAF rules which went into effect last March, athletes who miss three doping tests in an 18-month period are suspended for a year. Refusal to attend a doping test leads to an automatic two-year suspension.
IAAF testers were unable to find Kenteris and Thanou when they turned up in Tel Aviv to test them on July 27 and 28 this year.
The pair also missed an IOC test scheduled for Chicago on August 10 and 11 and again in the Olympic village on August 12.
The IAAF has already met IOC and Greek authorities to assemble evidence. "We have to know if the alleged missed cases are missed cases," Davies said.
The Doping Review Board will also examine the role played by coach Christos Tzekos.
"Under IAAF rules, a coach can also be sanctioned for a doping offence," Davies said.
The Doping Review Board will comprise IAAF president Lamine Diack, senior vice-president and IOC medical commission head Arne Ljungqvist, and council member Bob Hersh, a U.S. lawyer.
