Lewis has been a long-standing critic of Sir Keir and in November became the first Labour MP to call for him to stand down.
He admitted that at one stage this week he thought “this was it”, but believed it would only be a matter of time before Sir Keir was either forced or agreed to stand down.
“It’s a bit like having a gangrenous leg,” he told presenter Amelia Reynolds. “You can hobble around on it for quite a while, but at some point you need to sort it out.
“It’s painful, but you need to do it, and if we don’t do that, then I don’t believe that we’ll do anything other than hobble around, and that will be disastrous for the country and the party.”
He said there needed to be a change in the way Labour did politics, and said its culture and proximity to wealth and power had changed the way many people viewed the party.
He asked: “Is Keir Starmer the person to make the change? I think there is an argument that he isn’t… don’t ask me who the person is to do that, but what I do know is that the public is crying out for a government which will do the things which it set out to do.
“I am not undermining the party, I just want Labour to do what it says on the tin.”
Lewis also said he did not think Sir Keir’s appearance before Labour MPs on Monday had turned things around for him.
“There were lots of people giving him a standing ovation who I know didn’t mean it,” he said.