The Y&R-owned headquarters at 285 Madison Ave. is quietly being shopped for redevelopment and could fetch well over $100 million.

As The Post first reported yesterday, ad giant WPP is getting serious about finding a new home for Y&R, and negotiations are underway at 3 Columbus Circle through its broker at CBRE.

That would leave its current, 1926-era building on the northwest corner of 40th Street vacant and ready for a new life — likely as a hotel. The building, purchased by Y&R formerly Young & Rubicam in 1983, has been shopped to several investors over the summer, according to sources.

“It’s a great piece of real estate, and someone will see the value,” said Craig Nassi, head of BCN Development. CBRE declined comment.

Its 21,821 square-foot lot size, low ceilings and columns leave it ill-suited for offices. But it could be redeveloped into a well-located hotel in the shadow of Grand Central Terminal.