Television pictures showed the despondent Crewe-born athlete dropping to his knees with his head in his hands after being informed of his mistake, with several of his fellow swimmers offering their support.
‘Oh no, Luke’s gone too far. Oh no. Oh, that hurts. Oh, I’m so sorry. That really hurts,’ the BBC’s Andy Jameson said on commentary.
‘I believe it’s for going too far under the water. Oh dear, I’m so sorry. That’s really tough because it was brilliant commitment from an outstanding swim. He gave it everything.’
As a result of the blunder, Greenbank’s Team GB team-mate Oliver Morgan moved from sixth to fifth to qualify for this evening’s semi-finals at La Defense Arena.
‘I don’t know what to say, I’m absolutely gutted,’ Greenbank said shortly after the race.
‘It’s really annoying, I feel like I’m on good form.’