Smith, the Cowboys' first-round draft choice, injured the knee at the end of Wednesday's practice and his status for Sunday's season opener at the New York Jets is uncertain. He was wearing a knee brace as he watched other linemen work on individual drills.
Jermey Parnell, who has never played in an NFL regular season game, practiced with the first-team offensive line. Parnell has gained the confidence of his teammates and coaching staff that if he does start, he'll hold his own against the Jets' defense, which tied for eighth in the league with 40 sacks last season.
"I thought he did a nice job," coach Jason Garrett said of Parnell's work in practice Thursday. "Got more and more comfortable as he's gotten more reps. He's a guy who is very talented. He's a big guy, he's very quick and athletic and he's understanding how to play football more and more each day."
The Cowboys did receive some good news Thursday. Starting cornerback Mike Jenkins, who also hyperextended his left knee in practice Wednesday, returned to practice on a limited basis and said it feels better.
Jenkins missed the entire preseason while recovering from a stinger. As he enters his fourth NFL season, Jenkins has missed only two games due to injury, both during his 2008 rookie season.
"It's always something," Jenkins joked when asked about his health this summer. "I don't know what it was. I'm good. It was just football. A little injury. Got it checked out, and I'm ready to move on. I'm good to go."
But even that's uncertain, because even after team owner Jerry Jones ruled cornerback Terence Newman (groin) out vs. the Jets, the veteran looked good during a rehab session Thursday morning.
Newman ran hard laterally and showed a nice burst when moving forward, but it'd appear giving Newman another week might be helpful.
"Looks like he's moving around a little bit better," Garrett said of Newman.
Wide receiver Miles Austin (hamstring), center Phil Costa (knee) and Jenkins were limited in practice with injuries. Tight end Martellus Bennett (ankle) and newly signed wide receiver Laurent Robinson (hamstring) did not practice.
"They really are all day to day," Garrett said. "That's the best way to describe them. They're trying to work and get back, and how much they're going to be able to practice this week is something that we'll evaluate individually. But they're all pointing towards trying to be ready for the ball game on Sunday night."
Calvin Watkins covers the Cowboys for ESPNDallas.com.