Mano Polking on Saturday dropped young Port striker Teerasak Poeipimai to trim the national squad to permitted number of 23 players for the AFF Mitsubishi Electric Cup 2022, which starts on Tuesday.
The War Elephants flew to Malaysia on Saturday night to kick off the defence of their Southeast Asian crown against Brunei Darussalam on Tuesday night.
Thailand have been placed in Group A for the first-round, round-robin action. The other teams in the pool are Cambodia, Indonesia and the Philippines.
Polking will be without some of the leading names and the War Elephants will bank on the experience of veteran striker Teerasil Dangda and left wing back Theerathon Bunmathan to lead their campaign.
Among those missing from the team are prolific Buriram United strike duo of Supachai Chaided and Suphanat Mueanta, J-League-based Supachoke Sarachat, Port defender Thanaboon Kesarat and Bangkok United midfielder Thitiphan Puangjan.
The Thais played two warm-up games to prepare for the biennial Asean championship.
While they hammered Myanmar 6-0 in the first game on Sunday, Thailand suffered a shock 1-0 defeat to Taiwan in second on Wednesday at Thammasat Stadium, a result that Polking labelled as "disappointing".
The top-two teams from the two groups will qualify for the semi-finals, the first legs for which take place on Jan 6 and 7 and the second on Jan 9 and 10.
The home-and-away final is scheduled for Jan 13 and 16.
Domestic football leagues in the country are currently taking a break for the World Cup and the Asean championship with Thai League 1 returning on Jan 21.