The double Olympic champion, whose preparations for the World Championships - which start today - have been disrupted by injury, shrugged off the suggestion that he has not been able to recover full fitness.
"I am ready to run fast," said Johnson, who recorded 45.02sec in a comeback race in Houston, Texas two weeks ago. Referring to Reynolds' record of 43.29, he added: "The world record is under threat any time I'm in shape. And I'm in shape now."
Johnson's presence, on a wild card, after he had missed the US trials has generated controversy among athletes and officials. If his confidence is not misplaced, it is bad news for Britain's 400m challenge with Iwan Thomas hoping to lower the national record he set last month, and the relay team aiming high.
Johnson dismissed his poor performance in Paris on 25 June, when he lost his eight-year unbeaten record over 400m as four runners came past him in the final 30 metres. "That's what happens when you try and run fast and you are not in shape," he said.
There has been an encouraging report on Ashia Hansen, Britain's triple jump medal prospect, who begins her competition in the Olympic Stadium this morning. "She has had some treatment and the good news is that she is as bright as a button now" said Britain's chief coach, Malcolm Arnold. "I wouldn't say she's quite 100 per cent but her body language is good."
Dalton Grant, Britain's former European indoor high jump champion, has had to delay his flight here until Sunday, the day before his qualifying competition, because he is suffering from food poisoning.
Britain's athletes were encouraged on the eve of competition by rousing speeches from the British Athletic Federation president and former Olympic champion, Mary Peters, and the new team captain, Roger Black.
"No one here is a good athlete," Black told them before adding "You are all excellent athletes. That is why you are here."
His team-mates now have the opportunity to live up to his expectations.