Sprinter Justin Gatlin must serve at least four years of his doping ban, an International Association of Athletics Federations (IAAF) spokesman has said.
The US Olympic and world 100m champion was banned for up to eight years on Tuesday after agreeing that his positive drugs test constituted a doping violation.
Gatlin also agreed to help fight drug abuse in the sport, and the actual length of his suspension will be decided by an arbitration panel.
"Four years would be the minimum," IAAF spokesman Nick Davies told the BBC. "We want to see if it leads to other convictions. We want him to tell the truth about what really happened. If Gatlin just says `I don't know what happened,' that's not good enough."
The 24-year-old Gatlin, who has lost his share of the 100m world record, tested positive for the male sex hormone testosterone at the Kansas Relays in April for reasons he said he did not know.
It was his second positive test, which under anti-doping rules could have resulted in a life ban.
Gatlin has said he would contest the eight-year ban he received for doping and hopes to be back in action "as soon as possible", his lawyers said on Wednesday
Whilst he cannot now contest the validity of the April test which he failed, Gatlin can ask the USADA for the eight-year ban to be reduced on the grounds that he did not knowingly take the drugs.
"USADA has announced the sanction it intends to seek, but Justin has not accepted that recommendation and will go to arbitration," Gatlin's lawyer Cameron Myler said.
"He will argue that `exceptional circumstances' existed in this situation that justify a significantly better result than eight years. Our goal is to have Justin back on track running as soon as possible."
Gatlin, who also forfeited his share of the 9.77 seconds 100m world record by accepting the result of the drugs test, has six months to put his case for the eight-year ban to be reduced.
His lawyers did not say what their strategy would be, but the sprinter's controversial coach Trevor Graham claimed that the infraction had been due to the revenge actions of a masseur who applied testosterone cream on him without his knowledge.
The masseur has strenuously denied that claim and Gatlin's legal team at the time said Graham had spoken without their authority.