The 2009 Thai League Division 1 has 16 teams.

Nakhon Sawan Reprieve after Army Welfare Department withdrew Thailand Premier League 2008 Thailand Division 2 League Thailand Premier League 2008 Thailand Division 2 League Thailand Division 2 League Bangkok Bank FC withdrew from the league before the season began.

FAT therefore decided that to fill the league with 16 teams, they would run a pre-season competition featuring the 4 relegated clubs from the Thailand Division 1 League 2008 season.

The winners of the Pre Season Playoff would fill the void left by Bangkok Bank FC, after they withdrew from the league after being relegated from the Thailand Premier League.

The four semi finalist's in the play-offs, are the four relegated clubs from the 2008 season of the Thailand Division 1 League.