Separate Logo from Background (same colour)

Hi,

How would you separate a logo from a white background if elements of the logo were also white?

Imagine a blue 2D circle on a white background. The blue circle has a diagonal white line running through the circle all the way to the outer edges. Ordinarily I would just use the Magic selection tool and copy the whole logo to a new layer, but in this scenario the diagonal white line running through the logo cannot be selected without selecting the white background as well. 

Any help would be greatly appreciated.