IRVING, Texas -- Dallas Cowboys coach Jason Garrett walked to the podium for the first time with a concerned look. He quickly smiled when the questions came, but Wednesday was not a good day for the first-year coach.

The Cowboys suffered two injuries during Wednesday's practice that have raised concerns about the depth of the team.

First-round pick Tyron Smith, a right tackle, suffered a hyperextended knee toward the back end of practice, creating a tense situation on the offensive line that already has two rookies starting and another with one career start.

Before Smith was injured, starting cornerback Mike Jenkins suffered a knee injury in the early stages of practice, causing him to leave.

The status for both players is shaky with the season opener coming Sunday night against the New York Jets.

Jenkins already was battling nerve damage to his neck area that forced him to miss the entire preseason. He was on his way to playing in the opener until this latest scare.

His status is day to day and he could practice on Thursday because the injury is not as serious as originally thought.

An MRI revealed no structural damage to Smith's knee and he hasn't been ruled out for Sunday's game. Like Jenkins, he could practice on Thursday.

"There are different challenges that we all face every day," Garrett said. "If any of these guys aren't able to play, hopefully the backups understand the value of their opportunity and we can move right along."

The backups are a question.

If Smith is unavailable to participate, the Cowboys would turn to Jermey Parnell, who won a roster spot as the swing tackle in training camp.

Parnell has never played in a NFL regular season game and spent last season on the Cowboys practice squad.

After playing 30 college basketball games at Ole Miss, Parnell switched to football and played only one season before signing as an undrafted free agent with the New Orleans Saints in 2009. He was on the Saints practice squad in 2009 and last year spent time on the rosters of New Orleans and Miami before the Cowboys signed him last Oct. 14.

"Tackle is tackle," Parnell said of which side he prefers as he walked to the shower area after practice on Wednesday afternoon.

"I go against him every day in practice so I have a lot of confidence in him," outside linebacker DeMarcus Ware said of Parnell. "He runs block really well but his pass block is really quick. They stick him at right tackle, he's going to be a little quicker than a right tackle. He's already used to the speed. He's just got to get used to the bigger guys on that right side powering him."

Derrick Dockery, who was signed this week as a backup guard, could also get some practice snaps at tackle. But Dockery hasn't played tackle in an NFL game and hasn't done so since his days at the University of Texas.

David Arkin, a fourth-round pick, is another backup guard, yet he too could see time at tackle, if necessary. Arkin hasn't played tackle since part of his junior and senior seasons at Missouri State.

The injury to Jenkins is compounded by the loss of cornerback Terence Newman, who will miss Sunday's game with a groin injury.

At worse, the Cowboys were hoping for Jenkins to start with Orlando Scandrick, the talented nickel corner, who just signed a five-year contract extension. If Jenkins is out, then Scandrick will start with Alan Ball, who started 16 games at free safety last year for the Cowboys, but struggled at the position, allowing seven touchdown passes.

Ball, a seventh-round pick from Illinois in 2007, is more suited to play cornerback and he's had a strong training camp and preseason at that position.

"Very athletic guy," Garrett said. "He's long, he's quick, he's fast. He's a real competitor as well. He's really had a good training camp for us."

The Cowboys entered the 2011 season with five cornerbacks but injuries to Jenkins and Newman has lowered that number. Bryan McCann, a second-year player from SMU, would move into the third cornerback spot on the depth chart if Jenkins and Newman are out.

It's not an easy situation to be in for the Cowboys who move into the season opener with serious questions at key spots.

Of course, this latest health scare could be just that, if both players go on Sunday night. If not, young inexperienced players will get time at corner and tackle.

"I think a lot of our young guys, they had a good camp," quarterback Tony Romo said in a conference call with the New York media on Wednesday. "They're all working hard. You never know until you get out there, until you play in the games and see how it all pans out. All we can ask is that they work their butts off and they keep improving. That's what they're doing right now and they're doing a good job."

Calvin Watkins covers the Cowboys for ESPNDallas.com.