Rebecca Cooke became the latest British medal hope to fail at the World Swimming Championships as she finished seventh in the 800m freestyle final.
Cooke was also seventh in the 1500m freestyle final
Cooke, who won bronze in the event two years ago, was well off the pace as American Kate Ziegler took gold.
Canada's Brittany Reimer was second and Japan's Ai Shibata third, with Cooke more than 12 seconds behind Ziegler.
"I felt completely shattered. I was taken out in the first 100m and then I had nothing at all," said Cooke.
"I have been faster in training than I have ever been so I don't think it is due to fitness.
"It has not quite clicked. Maybe there is something there I need to look at. It is quite hard to pinpoint what is wrong.
"I will get some blood tests when I get home. Medical or not, I don't feel great."
Caitlin McClatchey's 400m freestyle bronze is the only swimming success for Team GB so far in Montreal.
Hopes now rest with David Davies, Liam Tancock and Kate Haywood going into the final day.