When the Mixed Ownership Model Act was passed late last month, Mr Key acknowledged the Maori Council's litigation posed a risk to the timetable for the Mighty River sale.
"That's always a possibility that could slow up the process," he said.
"The Government's view is that there's not merit to any litigation and that the issues of water which sit at the heart of any potential litigation have been well and truly covered through lots of other things we're doing, but I'm simply saying there's always a risk."
The Government is negotiating with the Iwi Leaders Forum over Maori rights and interests in freshwater.
But in its statement of claim, the Maori Council says the forum is not speaking on behalf of all Maori and the negotiations are taking place before all relevant Treaty claims have been heard.
State Owned Enterprises Minister Tony Ryall has said the Crown would cite the Ika Whenua case in 1990s, when the Appeal Court denied a bid to block a Government plan to transfer dams to energy companies because Maori rights would not be diminished.
THE CLAIMS
Wai 2357
Argues that partial privatisation of Mighty River, Meridian Energy and Genesis Energy would prevent Maori with valid but yet-to-be-determined claims over freshwater and geothermal resources from receiving stakes in the power companies as redress.
Wai 2358
Argues Crown actions and policies on freshwater and geothermal resources have breached the Treaty by using common law to alienate Maori from the resources. It also contends legislation such as the Resource Management Act does not adequately recognise Maori interests in those resources, and that Treaty policy doesn't provide adequate redress, such as compensation, or strong legal rights for Maori.