Four-time Olympic champion Mo Farah will consider his future after failing to qualify for this year's Games.
Farah, 38, missed the 10,000m selection time by 19 seconds at a cold and windy British Championships in Manchester.
He needed to go under 27 minutes 28 seconds to make the British team for Tokyo but finished in 27:47.04.
"I don't know what to think or what's next. If I can't compete with the best why bother?" said Farah, who won 5,000m and 10,000m gold in 2012 and 2016.
"There's no excuse in terms of conditions - it is what it is. I genuinely thought I'd come out here, get the time and then go back to the training camp.
"I've had an amazing career. Thinking about it tonight it's a bit shocking and I don't really know what to say.
"I'm lucky enough to have so many medals. I'm one of these athletes who, if you can't compete with the best, why bother?"
Farah's previous shot at qualifying for the Olympics, after more than three years concentrating on road running, was hampered by a left ankle niggle.
Reports from his high-altitude training camp in France were that his injury had cleared and his form improved since that Birmingham outing.
However, Farah could not maintain the necessary pace set by Australian duo David McNeil and Ryan Gregson.
Once Belgian training partner Bashir Abdi peeled off with nine laps to go, Farah steadily started slipping behind the required time as his stride shortened and a grimace showed on his face.
