(CNN)Britain's International Association of Athletic Federations (IAAF) presidential candidate Sebastian Coe says the prospect of American sprinter Justin Gatlin beating Jamaican Usain Bolt in the World Championships later this month makes him nauseous.
Sebastian Coe: 'Queasy' at idea of Justin Gatlin beating Usain Bolt
Gatlin has twice been sanctioned for doping offenses, but has recorded the fastest 100 meter time this year, while Bolt's form has been erratic. Both are Olympic gold medalists.
"I'm hardly going to sit here -- given everything I've said -- and say that I'm anything other than queasy at the thought of athletes that have served bans for serious infringement going on to win championship titles," said Coe, who is himself a double-Olympic champion.
In 2006 Gatlin was given an eight-year ban after testing positive for testosterone. The suspension was halved following his cooperation with the U.S. Anti-Doping Agency (USADA).
In 2001, Gatlin was suspended for two years after testing positive for an amphetamine found in attention deficit disorder (ADD) medicine he had been taking. That suspension was later reduced to one year.
"I don't like it and that's a very personal view. I have always believed -- and I'm fairly unreconstructed on this -- that lifetime bans for serious infringements are what we should have pushed for," said Coe.
"I also accept, because I live in the real world, that legally (banning athletes for life) would not hold," Coe said. "That train left the station.
"Gatlin is eligible to compete and he should be respected for the fact that he is eligible to compete," he added.
According to USADA figures, Gatlin has been tested 59 times since his return to athletics in 2010. Gatlin won bronze at London 2012 -- where Bolt completed his second successive Olympic treble, winning 100m, 200m and 4x100m relay gold medals.
In response to Coe's statements, Gatlin's representative Renaldo Nehemiah told CNN, "There is no comment to be made. I have great respect for Seb Coe."
Previously the U.S. sprinter has vehemently denied ever knowingly taking a banned substance and earlier this year, Gatlin said he didn't understand why he was often referred to as a "two-time drug cheat" -- a reference to his first ban.
Referring to his first ban, Gatlin recently told Reuters, "Other people in the sport have taken the same medication I had for ADD and only got warnings," Gatlin recently told Reuters. "I didn't."
And he told British newspaper the Guardian in May that he tested positive in 2006 because his massage therapist rubbed a testosterone cream on him without Gatlin's knowledge -- a claim the therapist denies.
A former middle distance runner, Coe currently serves as a vice president of IAAF, which has come under scrutiny over how proactive it has been in the fight against doping in athletics.
Allegations published in the Sunday Times earlier this month, and aired in a documentary by German broadcaster ARD, claim that a third of medals awarded in the Olympics and World Championships between 2001 and 2012 were won by athletes who recorded suspicious doping tests.
The news organizations based their reports on a leaked IAAF database, which holds the results of 12,000 blood tests on 5,000 athletes.
The IAAF has subsequently suspended 28 of those athletes, although most of them have already retired.
Coe stopped short at calling the allegations part of a witch-hunt, but did say that there was a concerted "portrayal of the IAAF ... as being a group of people who do not care about this.
"Our sport is about a great deal more than doping," said Coe, who will find out if he will become IAAF president on August 19. His opponent is former pole vaulter Sergey Bubka, also an IAAF vice president. Both have vowed to restore track and field's reputation.
"We've chased some of the biggest names out of the sport, and that doesn't come without a cost," he said. "The reputational damage to a sport for actually weeding out the cheats is actually quite profound, but we've still been prepared to do it because this is not a war we can allow ourselves to lose."
In 1979, Coe broke three world records within 41 days, an achievement that he admits would only raise eyebrows today. In fact, he says, it was even suspicious at the time.
"There had to be (doubts)," he said. "I came nominally from nowhere to break three world records, and of course people wanted to suggest that this wasn't done on anything (other) than hard work and natural talent. But sadly that is the world that top athletes in any sport live in."
"That is why I think moving to an independent anti-doping system is the next stage in really removing the perception," Coe said, choosing his words carefully.
"Not the reality, but the perception that there could be conflict and there could be cover-up," he added.