Without Deco, the Portugal NT really lacks a creative engine in the middle to put together good scoring chances. Ronaldo can score from the FKs and will be called upon to be the up-front creativity from the wings -- hopefully along with Ricardo Quaresma. But neither Gomes or Postiga are solid finishers (though Postiga has been better of late).
A lot will probably have to rest on the shoulders of João Moutinho, who has yet to prove himself in that role on the NT. Tiago hasn't been able to translate his club prowess to the NT, and Hugo Viana is a non-factor. Nani can be surprising, but he's not in his best form right now and seems to be better on the wings.
Ultimately, I expect a low-scoring affair, which should benefit Belgium. All it takes is a brain-dead defensive blunder by Caneira, Ferreira, or worst of all - Da Costa - and Belgium is in business. Carvalho and the returned Andrade are great in the center, but they can't do it all.