High-Point Rendel added that the management company behind the project, Campus and Stadium Ireland Development, lacked the experience to handle the project.
It says the scale and size of the facilities to be offered should be reconsidered.
The plan is for the stadium to host football, rugby and shooting events and to have a sports hall and arena that can handle up to 20 different kinds of sports. The project is still expected to form part of the Irish-Scottish bid for the 2008 European football championships.
A shortlist of five contractors has been compiled. These are believed to include consortiums led by Bovis Lend Lease and Multiplex, the Australian firm building the UK national stadium at Wembley.