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.
Mr Mnangagwa became head of state a year ago after Mr Mugabe was ousted following the intervention of the army.
Up to that point, Mr Mugabe was the only president Zimbabwe had known, having been in power for 37 years.
He led the movement for Zimbabwean independence from white minority rule. Image copyright Reuters Image caption President Emmerson Mnangagwa told supporters that his predecessor would be back in the country next week
President Mnangagwa was addressing a rally in his predecessor’s home area when he talked about the former leader’s health.
“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.
“We are looking after him. He is the founding father of the nation of Zimbabwe. He is our founding father of free Zimbabwe,” the president added, AFP reports.
The government is paying for Mr Mugabe’s treatment.
After taking over from him last year, Mr Mnangagwa won a disputed presidential election in July.