"We should not be pushed into a deal," Tsvangirai said.
"We would rather have no deal than get a bad deal. We have time on our side. We have the people on our side."
Mugabe has been threatening in recent days to name a cabinet without MDC officials.
The opposition says that would undermine the talks. Mugabe has yet to carry out the threat, raising the possibility he made it only to pressure Tsvangirai at the negotiating table.
Thabo Mbeki, the South African president, will meet Zimbabwe's rival parties in Harare, Zimbabwe's capital, on Monday in a new attempt to secure the power-sharing deal.
Ronnie Mamoepa, a spokesman of the South African ministry of foreign affairs, confirmed Mbeki's trip.
Tsvangirai beat Mugabe in a March 29 election but fell short of enough votes to avoid a June run-off, which was won by Mugabe unopposed after Tsvangirai boycotted it, citing violence and intimidation against his supporters.