Dallas Cowboys left tackle Tyron Smith had an up-and-down Wednesday, beginning his day with the high of being named the NFC's Offensive Player of the Week but later missing practice because of an ankle injury.

Even worse: Charean Williams of the Fort Worth Star-Telegram reports Smith underwent an MRI on his ankle, perhaps suggesting he's dealing with a serious injury.

Smith has been one of the NFL's best players through six weeks of play. He's opening lanes for DeMarco Murray, the NFL's leading rusher, and keeping quarterback Tony Romo upright despite challenges from some of the league's best pass rushers. If Smith were to miss any time, it would be a big problem for the Cowboys.