Former Khmer National United Party President Nhek Bun Chhay was released from prison under court supervision on Monday night and is likely to be re-appointed president of his party – a move fellow members hope will bolster the party’s chances in the upcoming national elections.

PJ Prison Director Pich Yun said Bun Chhay left the prison at about 9pm on Monday under orders from the Phnom Penh Municipal Court. He had previously said that he didn’t expect Bun Chhay’s release until Tuesday morning at the earliest.

“We were afraid [health] problems would happen to him if he is not released,” Yun said.

Current KNUP President Sing Kiri said on Tuesday Bun Chhay would reclaim his position as president once his health improved, though he declined to specify the severity or nature of the health problems. “Mr Nhek Bun Chhay will return to be president of the KNUP,” he said. “He needs to treat his health first and to relax to recover.”

Bun Chhay was arrested in August and charged with conspiracy to produce drugs and importing drug components in relation to a 2007 case. The arrest followed the leak of a purported phone call in June between Bun Chhay and then-Cambodia National Rescue Party lawmaker Eng Chhay Eang.

In the call, Bun Chhay appears to pledge to urge his supporters to vote for CNRP candidates in areas where the KNUP was not running. Given the time elapsed since the drug raid at the centre of the case, and the timing of the leak, the arrest was widely seen to be politically motivated.

Phil Robertson, deputy Asia director for Human Rights Watch, said if Monday’s release was on the basis of health, “it does help shift blame – because if he does indeed have serious health problems, the government can now argue they’re not to blame if his condition worsens”.

Da Chhean, a KNUP official at Thmar Puok commune in Banteay Meanchey, said Bun Chhay’s return was a game-changer, adding he expected to win one or two National Assembly seats with their leader back and the CNRP – once the country’s largest opposition party by far – controversially forced to dissolve by the Supreme Court late last year. “Everyone is absolutely excited and wants to visit him,” he said. “We are waiting for him to lead the party . . . This is the starting point again.”

Nheb Bun Chin, spokesman for the royalist Funcinpec party, which Bun Chhay once led, said he remained unconcerned about Bun Chhay’s return to competition. He claimed over 100 high-ranking members had defected from KNUP to Funcinpec, along with a large part of its active members. In Battambang, for example, he claimed 80 percent of KNUP members had joined Funcinpec, and in Banteay Meanchey – where the KNUP won a commune in last year’s local elections – about 60 to 70 percent defected.

Chhean, however, said those who had defected to Funcinpec were already returning to the KNUP – something Bun Chin denied. “I strongly believe they stay with Funcinpec,” he said. “Frankly, now he has only two months to go. How is he going to do it? Restructure the whole party?”

Ruling Cambodian People’s Party spokesperson Sok Eysan also remained unconcerned. “We do not worry [about competition],” he said.

But Mu Sochua, deputy president of now-dissolved Cambodia National Rescue Party, said Bun Chhay’s release was intended to superficially give legitimacy to a “sham election”.

“He will be forced to compete in the election so the CPP can say there’s competition and free and fair elections,” she said.