Michael Phelps of the U.S. looks up after his men's 200m individual medley heat during the London 2012 Olympic Games at the Aquatics Centre August 1, 2012.  [Photo/Agencies]

LONDON - American swimmer Michael Phelps is "probably not" the greatest Olympic champion of all time, despite winning a record total of 19 medals, London 2012 Games chief Sebastian Coe said on Wednesday.

Phelps eclipsed the previous record of Soviet gymnast Larisa Latynina's 18 medals, when the US won gold in the 4x200 metres freestyle relay at the aquatic centre on Tuesday night.

Coe, a former Olympic champion himself, said: "I think you can say it is self-evident that he is the most successful. I am not sure he is the greatest.

"It is a pretty good haul, but who is the greatest? In my opinion he is probably not."