Hammerson has been sent back to the drawing board over its plans for a£200 million expansion to Leicester's Shires shopping centre.
Two leading architectural watchdogs - English Heritage and the Commission for Architecture and the Built Environment (CABE) - spent two days in Leicester this summer, looking at plans for the city's regeneration.
They were invited by Leicester City Council, but urged a 'radical rethink' by developer Hammerson over a design that would double the size of the existing Shires Shopping Centre.
The extension was scheduled for completion in 2008, but the calls for a redesign could push that date back.
The two bodies concluded that the planned mall, department store and public square could be 'oppressive' because of its size and design.
The report said: 'Hammerson has made very positive contributions to the industry-wide move towards retail development that reinforces and enhances whole towns and cities. It might fail in that aim in Leicester without the radical rethink that the panel felt it must press for.'
Hammerson has said it will work with the watchdogs to 'make sure the application we put in meets their guidelines.' A council spokesman said the organisations would also work alongside CABE and English Heritage in a review.