The 26-year-old fell during the 800m semi-final and failed to finish the race. The setback came just weeks after he fell and broke his hand running in the Birmingham Grand Prix.
Learmonth, who had been named Great Britain captain heading into the Championships, said on Twitter: “This is so tough. I’m heartbroken and I can’t believe the same thing has happened twice in two weeks.
“But I’ll bounce back as quickly as possible. Thank you everyone for all the support this week.”
Learmonth also hit back at trolls on social media who had compared him to Elise Christie of the athletics world – the speed skater fell twice during Pyeongchang 2018 Winter Olympics races.
He said: “One more thing, to all the trolls calling me the Elise Christie of the Athletics world. Remember she’s a multiple World and European Champion. I hope one day I can be as half as great as, Elise. Thank you again, to absolutely everyone for all the warm and supporting messages.”
On captaining his country, he said: “It is an absolute honour to captain this 49 strong Britain Athletics team on home soil. I am rarely speechless but this one caught me by surprise. To those in this amazing team who voted for me, thank you. I am truly humbled. Great Britain, we will all give it everything.”
Great Britain finished second in the medal table, with the most medals in total (12). Poland had the most gold medals (five to GB’s four), meaning they finished top of the standings.