Thailand U23 coach Worrawoot Srimaka admitted that he had a lot of work to do after his men finished last in the Dubai Cup friendly tournament on Tuesday.
The young War Elephants lost 2-1 to Iraq in their final game in Dubai after being beaten 1-0 by Qatar and 4-2 by China in their first two matches.
Alexander Aoraha opened the scoring for Iraq after 16 minutes and William Weiderjoe equalised for Thailand just before half-time.
The Iraqis were the better side for long periods in the second half and Wakaa Jumaa finally scored the winner in injury time with a close-range effort.
"First of all, I have to apologise again," Worrawoot said.
He said there are several problems, particularly the players' fitness levels, to be solved ahead of the SEA Games in Vietnam in May and the AFC U23 Cup in Uzbekistan in June.
"We could see that our players' fitness levels dropped sharply in the third game of the tournament," Worrawoot said.
"The players' fighting spirit was there but their fitness was not. We need to improve our physical fitness. I am worried about the players' fitness. They moved quite slow in the match [against Iraq].
"The players understood our tactics but they could not perform according to our plan because of their fitness levels."
However, he said at least his players gained experience from playing in an international tournament.
Worrawoot added that the tournament gave him the chance to see which players are good enough to be the team's core members.
Thailand last won the SEA Games title in 2017.
At the 2022 Asian Cup, the Thais are in Group C along with South Korea, Vietnam and Malaysia.
