Design guru Wayne Hemingway has described plans to build a shopping park on the Frontierland site as “vague and lacking in detail”.
The Morecambe-born entrepreneur voiced his fears as it emerged that Lancaster City Council had asked developer Opus North to provide more information about the £17m seafront scheme.
Opus North wants to build a new modern retail centre called the Bay Shopping Park on the derelict ex-fairground site, creating 500 new jobs.
The Yorkshire-based developer is in talks with big-name chains and also wants to build a 62-bedroomed hotel and new family pub-restaurant.
There has been overwhelming support for the plans from residents and MP David Morris.
Opus North originally hoped the plans would go before Lancaster City Council in mid-September.
But a council spokesman said it would be later than that, as they wanted more details on “highways and traffic, retail impacts and elevational detail”.
Mr Hemingway, who runs London-based design firm Hemingway Design, said: “Of course, everyone should welcome the site coming back into use and the aspiration for decent retailers like Marks & Spencer and decent eateries.
“But if it comes back to life as a poorly designed, poorly detailed and executed development then it will be worse than it remaining empty.
“This is a strategically important prime site on the promenade of a British seaside town that is starting to turn the corner and should be treated with top class design thinking.
“The elevations and sketches that are in the public domain are so vague and lacking in detail, I fear there is a danger that little of the quality that the site deserves could end up being delivered.”
A spokesman for Opus North said: “More than 1,200 local people have contacted us to support our plans.
“Our development team is working closely with the council to get the plans absolutely right for Morecambe. The design will be contemporary, attractive and a credit to the seafront. As a result more people will enjoy shopping in Morecambe, stay longer and spend more money across the local economy.”
Meanwhile, David Morris MP has called for Lancaster City Council “not to drop the ball” on the plans.
Mr Morris said: “I am convinced that this plan to regenerate Frontierland is right for Morecambe.
“After 15 long years we finally have an exciting and viable scheme on the table.”
The West End Million Steering Group also added their voice to the chorus of support.
A spokesman for the group, who are in charge of £1m worth of Lottery funding awarded to the West End, said: “We see that the creation of jobs locally will have a beneficial effect on the economy of the West End.”
Owners of the rival Arndale Centre and developers British Land, who are planning a major retail development in Lancaster, have both objected to the scheme.
For more information on the plans go to www.futurefrontierland.co.uk or Lancaster City Council’s Planning Applications section at www.lancaster.gov.uk, reference number 14/00388/FUL.