McCaw has previously turned down the chance after the All Blacks won the Rugby World Cup in Auckland in 2011.
John Key told TV3's Paul Henry Show this morning he would get another offer.
"Whether he would take one, I don't know. The offer was there before and I can't imagine anything has changed."
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Mr Key also noted the "Richie for prime minister" banner at Eden Park the other night and said: "I thought, well, not a bad option really".
"He has got a massive brand and you think how successful Colin Meads is now and Richie is at the starting point of that.
"He's articulate, he's an intelligent guy, there's a range of things he could do. I don't know if politics is one of those options. He has a lot of business interests and I'd think he'd pursue one of those."
Later on TV1's Breakfast, Mr Key said, in his opinion, McCaw was the greatest ever All Black.
"As an athlete, you've got to say this guy is a freak."
McCaw is now the most capped rugby international, with 142 test appearances following New Zealand winning the Bledisloe Cup against Australia on Saturday night.
The World Cup beginning on September 18 and hosted by England will be his All Blacks farewell.