One of the architects who designed Federation Square has spoken out for the first time against plans to demolish one of the square's key buildings to build an Apple mega-store.

Architect Peter Davidson was one of two designers behind Federation Square when it was commissioned by then premier Jeff Kennett in the 1997.

Completed in 2002 amid much criticism, many have come to love the square's landmark buildings and public spaces.

Now, on the cusp of a decision on whether to allow one of the square's buildings to be demolished for Apple, Mr Davidson has voiced his opposition.