The contradiction suggested differences had emerged within his party over implementation of a September power-sharing pact that could add to uncertainty over whether a new Zimbabwean leadership would be united enough to tackle an economic crisis.
Regional leaders decided at the meeting on Tuesday that Zimbabwe should form a unity government next month but the MDC issued a statement saying it was disappointed with the outcome, raising doubts over chances of ending the political deadlock.
President Robert Mugabe, who has made it clear he would set up a government without the opposition if need be, said talks were concluded and a new cabinet could now be formed.
South Africa’s Star newspaper quoted Tsvangirai as saying that resolving outstanding issues over a government was a "work in progress".
"Everyone agrees that — subject to the clearing of all the issues that are outstanding — a coalition government can be formed," he said.
"After all, the whole idea of these negotiations is to form a coalition government, and I therefore agreed to that principle."
The 15-nation SADC grouping said after a summit in South Africa — its fifth attempt to secure a deal on forming a unity government — it had agreed that Tsvangirai should be sworn in as prime minister by February 11.
But the MDC quickly issued a statement after the SADC (Southern African Development Community) communique, making clear its disappointment and raising the possibility that deadlock would drag on.
The MDC said its national council would meet to define its position on the summit.
Zimbabwe’s state-run Herald newspaper said MDC Secretary-General Tendai Biti made a "sudden U-turn" over implementing the deal.
The signing of the pact was seen as a chance to prevent a total economic collapse that would add to the strain on neighbours already hosting millions of Zimbabweans who fled in search of work.
Others are escaping a cholera epidemic that has killed nearly 3,000 people and infected more than 56,000 since August — Africa’s worst outbreak of the disease in 12 years, according to World Health Organisation figures.