Double Olympic champion Mo Farah has claimed that victory in the London Marathon would be his greatest achievement.
The British athlete has never raced over the distance, and collapsed at the New York half-marathon last month.
Farah also revealed his excitement at testing himself against such a talented field of athletes.
"I'm as clueless as everyone else," he told reporters. "Yes, I've covered 20 miles and a little bit more in training but I haven't covered the full distance at that pace.
"Winning would be the greatest thing I have ever achieved. Not just in terms of the London Marathon title but in terms of the field and the people in it. To come away with a win would be up there, it would be incredible."
The race takes place over 26.2 miles on Sunday morning.