Nakhon Ratchasima look set to go down to Thai League 2 after suffering a 3-1 home loss to Police Tero in Thai League 1 on Sunday night.
With just one round of matches to go, the Swat Cats occupy the final relegation spot.
They have 39 points, three behind Prachuap and Khon Kaen. The defeat allowed Sukhothai and Lamphun Warriors to stay up.
Nakhon Ratchasima, with former Thai football chief Worawi Makudi as president, will now have to win at champions Buriram United and hope other results go their way.
Against Police, Nakhon Ratchasima's Patcharapol Intanee was sent off in the 34th minute for his foul on South Korea's Jeong Woo-Geun.
Marc Babo gave the visitors the lead in the 39th minute only for Jordan Murray to equalise just before half-time.
Five minutes after the restart, Jeong restored Tero's lead and Babo finished off the Swat Cats in the 71st minute.
Nakhon Ratchasima coach Teerasak Pho-on admitted that it was a tough task for his men to play with 10 players. "We will fight in the final match," he said.
In another game, Buriram United failed to win for the second game in a row after being crowned champions when they were held 1-1 by hosts Ratchaburi.
Arthit Budjinda opened the scoring for Buriram, who lost to Port at home last week, after just five minutes but Anon Amornlertsak equalised for the Dragons in the 25th minute.