Tyron Smith suffers hyperextended knee

Cowboys RT Tyron Smith went down with a hyperextended knee in Wednesday's practice.  He'll undergo an MRI, but it sounds like he'll be out 2-4 weeks.  Smith was slated to start for Dallas and will be replaced by Jermey Parnell, an undrafted free-agent who has never appeared in an NFL game.  It's a definite concern for QB Tony Romo, especially against Rex Ryan's Jets this Sunday night.