Smith was expected to get the start despite having an uneven preseason after Mark Sanchez was injured in the third preseason game versus the New York Giants. Sanchez laid on the turf for a few minutes before being helped off the field and is now day-to-day, but definitely out for the season opener.
As for Smith, the second round pick sat out the fourth preseason game to get some rest after throwing three interceptions versus the Giants. The ugliest play of his day was the safety taken by Smith, however, as he was rolling out and ran onto the end line (pulling a Dan Orlovsky, for those familiar with bad NFL quarterbacking).
Nobody is sure who will start once Sanchez comes back, but it's expected to be either him or Smith. Matt Simms and Brady Quinn are also on the roster, though, in case Smith should get hurt in his debut.