Former Democrat leader Chuan Leekpai has firmly opposed the party joining the Pheu Thai-led government amid concerns over declining popularity.
Mr Chuan reiterated his stance against participating in Prime Minister Paetongtarn Shinawatra's coalition. "I have to protect my dignity because I promised voters we would not join (Pheu Thai)," he said during an interview with CU Radio at Chulalongkorn University on Friday.
Despite Mr Chuan's resistance, the Democrats, led by Chalermchai Sri-on, appear poised to exit the opposition and join the coalition government. Former Prime Minister Thaksin Shinawatra acknowledged in the Vision for Thailand forum on Thursday that the government led by his daughter would include the Democrat members.
Democrat deputy secretary-general Chaichana Detdecho was also present at the forum, marking Thaksin's first public speaking engagement in Thailand in 17 years.
Speculation suggests the Democrat Party may receive two ministerial positions, with Mr Chalermchai as the Natural Resources and Environment Minister and another deputy position in a ministry for secretary-general Det-it Khaothong. These slots are considered part of the quota belonging to the deeply divided Palang Pracharath Party, under the leadership of Gen Prawit Wongsuwon, who may be excluded from the government.
Mr Chuan warned that joining the coalition would reduce the Democrats to a "spare party," filling the role previously held by Gen Prawit's faction.
"As an old generation, I strongly believe the Democrat Party has dignity and integrity," the 86-year-old politician said during the radio program. "The dignity and integrity of the party is no longer the same."
The country's oldest party won only 25 seats in the general election on May 14 last year.