Great Britain's Dwain Chambers believes Usain Bolt's form has given his 100m rivals encouragement that he can be beaten at the World Championships.
The world and Olympic champion goes into the event in Daegu, South Korea as only the sixth fastest in the world this year with a best of 9.88 seconds.
"Usain has shown this season that he is a human being," said Chambers.
"You never know what can happen. Every man has his day. We have to do our best when we are in that final."
Bolt set the world record mark of 9.58 in winning gold at the World Championships in Berlin in 2009.
Chambers, who has a best of 10.01 this season, added: "This guy has been dominant in ways that were unmanageable to us as athletes.
"The fact he has not been on top form does not put any doubts in my mind. He's still the number one contender. I wouldn't put anything past him."
Injury has played its part in Bolt's dip in form. An Achilles tendon problem brought a premature end to his 2010 campaign, while scoliosis, a curvature of the spine he has suffered from since birth, hampered him over the winter.
Bolt is unbeaten since losing to Tyson Gay in Stockholm last August - the American will be absent from Daegu because of injury - but the Jamaican's season's best is some way off compatriot Asafa Powell's world-leading 9.78secs.