South Korea captain Son Heung-min said he had been running on empty after his country's shock Asian Cup quarter-final defeat by Qatar, blaming exhaustion and insomnia.
The Koreans were stunned 1-0 in Abu Dhabi on Friday, once again failing to break a hoodoo dating back to 1960.
While Tottenham manager Mauricio Pochettino will welcome Son's early return, the Korean forward admitted after the game he had been struggling with his fitness.
"I wasn't fully prepared," revealed Son, who played three matches in the Emirates after arriving before South Korea's final group-stage game with China.
"I felt physically empty. I'm feel so sorry to have let down my team-mates, coaches and the fans."
Son appeared in a punishing 13 matches for Spurs since the start of December and immediately played 87 minutes in South Korea's 2-0 win over the Chinese.
Abdelaziz Hatim's late strike dumped the co-favourites out of the Asian Cup, extending their 59-year title drought.
As the Qataris celebrated wildly, Son admitted he had failed to sleep properly since arriving from London.
"I would rather not speak about it really but I haven't felt right physically," said the 26-year-old.
"I was losing sleep -- I should have looked after my condition better."
Running on adrenaline, Son provided the spark against China, winning a penalty and adding an assist.
But he looked off the pace as the Koreans were taken to extra time by Bahrain in the last 16 and failed to make an impact against 2022 World Cup hosts Qatar.
"I thought I would start to feel better and grow into the tournament but it just didn't happen," lamented Son as South Korea were eliminated before the semi-finals for the first time since 2004.
"Many people expected big things of us and I'm annoyed at myself for not being able to step up. I know I didn't perform well."
Son has represented South Korea in three tournaments over the past seven months -- also playing at last year's World Cup and Asian Games in Jakarta, where he helped them win gold and earned himself an exemption from military service.
South Korea, who famously reached the World Cup semi-finals in 2002, were looking to improve on their Asian Cup showing four years ago when they finished runners-up to Australia.
But after coming up short, Son has called for a period of self-reflection.
"The future of the national team will depend on how we deal with this result," he said.
"We need to keep in mind there are no teams in Asia we can just expect to beat easily. We need to improve."