British medal hope Euan Burton broke down in tears after his -81kg campaign ended as he lost his first contest to Canadian Antoine Valois-Fortier.
Given a bye to the second round, Burton was beaten by ippon.
The 33-year-old said: "I feel like I've let myself down, let my coaches down, let everybody I've ever trained with down, let my mum and dad and brother down."
No British male has won a judo medal since Ray Stevens in 1992.
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“I am disappointed for myself, but more gutted for everybody else. I can live with the fact I put it all into training to be the best judo player ever”
Burton, who won bronze at the 2007 and 2010 World Championships, added: "I've been working for this for over a quarter of a century; there are no positives to be taken from it.
"I don't know if it's the end of my competitive judo career but it's probably the end of my Olympic career. I'm pretty sure you won't see me in Rio [in 2016].
"I wish I could have done a bit more for the people who have come down and watched, and I know I could have done."
Valois-Fortier, 22, beat Azerbaijan's Elnur Mammadli - the European champion and -73kg Olympic gold medallist at Beijing 2008 - in his opening fight on Tuesday.
That victory caused some surprise among members of the media, although they were less shocked when the Quebec-born talent toppled Burton.
Burton, for so long Britain's most consistent performer, finished seventh in Beijing four years ago.
Britain's last Olympic judo medal came when Kate Howey claimed silver at Sydney in 2000.