Labour health spokeswoman Annette King said a document she obtained revealed the board was in ''serious freefall'' with a ballooning deficit.
The document shows a $27 million deficit in 2014-15 and a $42 million deficit projected in 2015-16.
''The [National Health Board] advised the DHB that this [deficit] is unacceptable,'' the paper says.
Cost-cutting proposals would be considered by the board this month and next month, the paper shows.
The Ministry of Health had advised Dr Coleman on ''governance options'' for the board.
Mrs King said the governance options were not specified, but she believed it meant a commissioner was being considered.
''When they talk about governance options, there aren't that many options.''
Mrs King supported some form of intervention.
''They need more than a commissioner to run the cuts.
''They need somebody to find out why this board is not able to reduce their deficit or live within the budget.''
Nelson Marlborough DHB chief executive Chris Fleming was finalising a report about the board following his ''recent peer-support role'', the paper said.
The chairman role has been the subject of speculation in the sector because of perceived difficulty finding someone willing to take the role.
In February Dr Coleman confirmed he was replacing Joe Butterfield, but more than two months later, no replacement has been named.
A spokeswoman for Dr Coleman said he intended to appoint a new chairman, rather than install a commissioner.
In a written statement, Dr Coleman said Mr Fleming, an experienced senior manager, was providing ongoing support to the board.
''A growing deficit at Southern DHB is not acceptable. The ministry is working closely with the DHB and it remains on intensive monitoring by the National Health Board.
''Given that Dunedin Hospital requires extensive redevelopment, it is important the DHB returns to a more sustainable financial position whilst ensuring the delivery of effective services that meet the community's needs.''Joe Butterfield is still SDHB chair up until the point at which a new chair is appointed, and that will occur in due course,'' Dr Coleman said.
The paper comes as the board's community-based health providers are reeling from a proposed 5% cut to their funding. The board is negotiating 2015-16 contracts and reportedly told a large number of organisations, including rural hospitals and mental health and addiction providers, that it needs to cut 5% from contracts.
The health board yesterday declined to comment on the leaked document. Asked about the proposed community funding cuts earlier this week, it said it was working to ensure services were delivered as efficiently as possible.
