Mnangagwa, who is in Rwanda attending an extraordinary summit of the African Union, said the 94-year-old Mugabe is now forgetful due to advanced age and should not be taken seriously, state-run news agency New Ziana reported.
Mnangagwa was responding to a question on media claims that Mugabe may not vote for him in elections set for mid year.
“The former president is our founding father, we respect him. He is now 94 and he is bound to forget what he says,” Mnangagwa said.
“If you ask him again, he will tell you I will support ED (Mnangagwa’s initials),” he said.
Mugabe last week granted a media interview in which he complained that he was forced out of power through a “military coup.”
In the televised interview, his first since his resignation last November, Mugabe claimed Mnangagwa’s administration was illegitimate and indicated his willingness to meet with the new president to resolve the matter.
Mnangagwa responded to Mugabe’s claims, saying the nation had “moved on” and was now preoccupied with preparations for polls.
There have been media reports also linking Mugabe to the newly formed opposition National Patriotic Front, which is believed to comprise members mainly from the so-called G40 faction fronted by the former first lady Grace Mugabe.