Lord Coe has refused to call Michael Phelps the greatest Olympian of all time - despite the American winning more medals than any other athlete in history.
Yesterday the 27-year-old claimed his 19th medal, making him the most decorated Olympian ever.
Although the Baltimore-born swimmer is "up there" with the Olympic greats, the London 2012 chairman said he did not consider Phelps to be the greatest.
"Self-evidently, by the medal tally, he's the most successful," said Lord Coe.
"My personal view is that I'm not sure he is the greatest. But he's certainly the most successful, that goes without saying."
He continued: "In the lead-up to these Games we have talked about the great British pub game of picking who is going to be lighting the cauldron and all that sort of stuff.
"This is the global pub game: Who is the greatest Olympian of all time? It is self-evident, the guy has won how many medals, 19? It is a pretty good haul, but whether he is the greatest, I don't know.
"But you have to say he's up there. But whether he is the greatest, in my opinion, probably not."
Lord Coe shied away from naming the athlete who he thought deserved the title.
He said: "I could throw out a series of names, I could throw out Steve Redgrave, I could throw out, domestically, Daley Thomspon. If I wanted to go back a few generations I think what Jesse Owens did in '36 was unbelievable or Nadia Comaneci.
"I don't know. It is the global pub game."
Phelps became the most successful athlete in the history of the Games yesterday when he won gold in the men's 200m freestyle relay, bringing his all-time tally of Olympic medals to a record 19, one more than Soviet gymnast Larisa Latynina.
Phelps has 15 gold, two silver and two bronze medals.
He still has three races to come in the Games and could finish his Olympic career with 22 medals.