Almost 1,000 people have died in the cholera outbreak, piling more agony on Zimbabweans already suffering runaway hyperinflation and shortages of food and fuel.
The cholera has intensified calls for President Robert Mugabe, who has ruled since independence from Britain in 1980, to step down.
He said the decision was made by a troika of SADC (Southern Africa Development Community) countries that has been dealing with the Zimbabwe crisis.
SADC has been pushing Mugabe and opposition leader Morgan Tsvangirai to implement a deal to form a September power-sharing government, but they have been deadlocked for months over ministries as Zimbabwe descends further into chaos.
Motlanthe said he hoped the power-sharing government would be finally formed this week.
But Nelson Chamisa, spokesman for Tsvangirai’s Movement for Democratic Change, said they knew nothing of a breakthrough this week.
"Maybe the president knows something we don’t know, but we are not aware of any plans to form a government this week. It’s certainly news to us because the outstanding issues we have outlined remain."
Motlanthe added that he would not join calls for Mugabe to step down, saying the power-sharing deal would keep him as president, with Tsvangirai as prime minister.
He said he expected Tsvangirai to accept the prime ministerial role.
"He has always committed himself, he regards himself as the prime minister-designate, therefore I think once appointed he will accept."