Speaking to News24 on Wednesday, Chamisa said the ruling out of opposition parties was a missed opportunity at rebuilding the country and ushering in unity.
"It is a tragedy and very disappointing that he does not want to work with the opposition. He should have roped in the opposition in his new government in order to build unity and trust. We're very disappointed that he missed that chance," said Chamisa.
Chamisa's remarks came a week after Mnangagwa had visited the MDC's ailing leader Morgan Tsvangirai, during which he ruled out the possibility of a unity government, saying "currently there is no need".
READ:EXCLUSIVE: Chamisa says he is ready to lead' after Tsvangirai exit
Tsvangirai was prime minister in a unity government between 2009 and 2013 after he beat Mnangagwa's predecessor and mentor,Robert Mugabe, but not with enough votes to avoid a second round.
"We had previously worked with Zanu-PF in the unity government and the key thing here is not who we work with, but we want to advance the interest of our country. We were willing to advance the interest of our people," said Chamisa.
He added that Mnangagwa's visit was also aimed at discussing various issues regarding the upcoming elections.
"Well, the visit was also about the elections. We told him that we want to see a credible election and transparent vote.We've also told him we want to see a demilitarised electoral body, and as a matter of fact we don't want to see another election that is rigged," said Chamisa.
Justice Minister Ziyambi Ziyambi recently said that there was no need for major electoral reforms. "Everything that they are complaining about is clearly covered within our constitution and our laws," he was quoted saying.
Ziyambi said that the country's controversial electoral body was independent and was "not subject to the control of anyone".
He added that Zimbabwe's laws are in line with those of the African Union and the Southern African regional bloc SADC.