"There is a huge avalanche of calls and pressure from supporters across the country, especially in the rural areas, not to accept to be participants in this charade," Chamisa told the Reuters news agency.
He said the MDC would announce its decision on Monday.
Tsvangirai has been detained by police five times as he has attempted to campaign, and the MDC says that at least 70 of its supporters have been killed in election violence.
Bennett acknowledged that the poll on June 27 would not be free and fair but said that the violence showed how important it was to stand against Mugabe.
"On the backdrop of that we have to compete in these elections to show the total illegitimacy of them," he told South Africa's independent e.tv television news.
Innocent Gonese, the MDC's secretary for legal affairs, appeared to agree with Bennett.
"People are saying despite all that we should not withdraw and we also believe withdrawing will not solve anything," he told the AFP news agency.
If Tsvangirai were to pull out of the second round poll it would hand victory to Mugabe, who on Friday said that "only God" could remove him from office.
|A judge refused calls for treason charges against Tendai Biti to be dropped [AFP]
Mugabe has led Zimbabwe since independence in 1980 but is facing his most serious challenge ever in next week's poll.
"The MDC will never be allowed to rule this country - never ever," Mugabe told local business people in Zimbabwe's second city Bulawayo on Friday.
Later he told a rally in the same city: "We will never allow an event like an election reverse our independence, our sovereignty, our sweat and all that we fought for ... all that our comrades died fighting for."
Mugabe's government also attacked former colonial power Britain saying it was trying to bribe African leaders to condemn the election because of fears Tsvangirai would lose the vote.
"True to fashion, prime minister Gordon Brown is going back to the old habit of divide and rule," Olivia Muchena, science and technology minister, said on state television.
Muchena's remarks came after Brown said: "I think we have to remind President Mugabe and the Zimbabwean regime that the eyes of the world are on what is happening in that country."Treason charges
Meanwhile, a Zimbabwean magistrate on Friday refused to throw out a treason charge against a senior MDC member.
Mishrod Guvamombe ruled on Friday that Tendai Biti, secretary-general of the MDC, would remain in custody until July 7.
"Taking into account all submissions, I'm of the view that there is reasonable suspicion to believe the accused committed the said offenses. Accordingly the application is dismissed," Guvamombe said in a Harare court.
Biti was first taken to court on Thursday to hear the charges against him, which include subversion and vote rigging.
The charges could carry the death penalty.