Roy Bennett, picked to be deputy agriculture minister in the administration, was arrested before ministers were sworn in last Friday on charges of illegally possessing firearms for purposes of trying to commit acts of insurgency, banditry and terrorism.
His lawyers failed on Wednesday to have terrorism and insurgency charges dropped against him.
New Zimbabwean Prime Minister Morgan Tsvangirai said on Wednesday Bennett’s arrest undermined the government and efforts to stabilise the economy.
He has also demanded the release of other party activists, including human rights campaigner Jestina Mukoko. But the MDC has not taken actions that could threaten the new government.
"They (the MDC) are not doing enough at all — no. Roy has been there (jail) five or six days. As far as I am concerned he is no better off in there under a coalition government than he was under a ZANU-PF (Mugabe) government," Bennett’s wife, Heather, said in a telephone interview with South Africa’s eTV.
Zimbabwe’s MDC may be reluctant to quit the new unity government formed to lead the country out of economic crisis, despite Bennett’s arrest, senior party official Tendai Biti, the new finance minister, said on Monday.
"Surely it’s a very simple case. Roy should at least be released on bail and if there was a case to answer to let him come before a court. Apart from that surely the inclusive government has to respect the rule of law and human rights.
Mukoko and opposition activists have been charged with attempting to topple Mugabe and have been in detention for more than two months, deepening tensions in a new administration.
They deny the charges and say they were tortured while in police custody, allegations authorities deny.