The rapidly dwindling number of judges at the country's Constitutional Court could throw Park a lifeline, after millions of people have taken to the streets to demand her resignation and she was impeached by parliament last month.
Pak Han-Chul will retire as the court's chief justice next week at the end of his six-year term, with another of his colleagues following suit on March 13.
That will leave the court with only seven sitting judges, but by law six votes -- a two-thirds majority of the full court -- will still be needed to uphold Park's removal from office.
The outgoing judges will not be replaced until a new president is elected.
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The absence of two justices "could seriously distort the court's decisions", warned Park Han-Chul, who was appointed by the impeached politician.
The president was impeached over a corruption and power abuse scandal centred on her friend and confidante Choi Soon-sil.
The Constitutional Court has until June to decide whether to approve the decision, in which case new elections must be held within 60 days, or reinstate her.
Moon polled 29.1 per cent against Ban's 19.8 per cent, followed by another Democratic Party runner Lee Jae-Myung with 10.1 per cent.