Mr Mugabe has been in Singapore for treatment for an undisclosed illness for the past two months, he added.
The former president also made several medical trips there towards the end of his time in power.
Up to that point, Mr Mugabe had been in power for 37 years, first as prime minister, then as president.
He led the movement for Zimbabwean independence from white minority rule.
“He is now old. Of course, he now is unable to walk but whatever he asks for we will provide,” the AFP news agency quotes him as saying.
When Mr Mugabe was in power officials said he was being treated for eye problems, denying rumours that he had cancer.
Despite being unable to walk, Mr Mnangagwa said the former leader was feeling better and would be back in the country next week.