Thailand coach Kiatisak Senamuang has warned his men to stay fit or be ready to get punished by Myanmar in the two-leg 2016 Suzuki Cup semi-final.
The first leg of the semi-final will take place at Thuwunna Stadium in Yangon on Sunday and the defending champions Thailand's home game will be at Bangkok's Rajamangala National Stadium next Thursday.
Kiatisak said he was expecting two tough games against a "fit and strong" Myanmar side, which finished second in Group B after edging Malaysia 1-0 on Saturday night.
The other semi-final will pit Group B winners Vietnam against Indonesia, who finished second behind Thailand in Group A, on Saturday and next Wednesday.
The Thais won their three first round games to finish with a perfect nine points, the same as Vietnam in Group B.
Kiatisak added: "The away game is likely to be a tough one.
"This Myanmar team is good. They have a good mixture of veterans and players from their youth team which reached the Fifa U20 World Championship last year.
"They have good speed when attacking from both wings and striker Aung Thu, who is just 20, is also quite good.
"We cannot underestimate them at all and they will have a big support from the local crowd in the first leg which can inspire them to do something special."
Kiatisak insisted that fitness will be the key to winning the semi-final battles.
"We must prepare ourselves well and our fitness must be very good. Our mission is not yet finished.
"If we are not fit, we may get punished by Myanmar. They just showed us what they they are capable of when they beat Malaysia."
The biennial Suzuki Cup is considered the Southeast Asian championship.