KNOXVILLE, Tenn. (AP) — Tennessee already is encountering a couple of obstacles in its attempt to revitalize a pass rush that has been dormant for several years.

Senior defensive end Jacques Smith has a fractured right thumb that is expected to sideline him for four to six weeks and freshman defensive end Corey Vereen is undergoing an MRI on his knee. Those injuries could force the Volunteers to open the season without two of their most promising pass rushers, though Tennessee coach Butch Jones hasn't ruled Smith out for the Aug. 31 opener against Austin Peay.

"It lends itself to more players getting an opportunity," Jones said. "We have some veterans at that position who have played a lot of football here. ... We have a standard of expectation at a position that will never change no matter who's out there playing for us."

Tennessee is trying to upgrade a pass rush that has produced a combined total of 33 sacks over the last two years. Tennessee had just 17 sacks last season and ranked 13th out of 14 Southeastern Conference teams in sacks per game.

The Vols have said throughout training camp that they planned to put more pressure on opposing quarterbacks this season. They aren't backing down from those predictions now.

"We had a meeting today about having adversity happen in any type of situations," senior defensive end Corey Miller said after Wednesday night's practice. "Third-and-long, fourth-and-2 at the goal line, making a big stop, having the offense (turn over) the ball and having to go back on defense. Adversity is going to strike at any given time. We're always going to be prepared for it."

Tennessee opened training camp with seniors atop the depth chart at all four spots on the defensive line: Smith, end Marlon Walls, tackle Daniel McCullers and nose tackle Daniel Hood. Miller and Maurice Couch give the Vols two more senior linemen competing for starting jobs.

There's plenty of experience. There just hasn't been much production up to now. Smith's 4 ½ career sacks are the most of anyone on Tennessee's roster.

The Vols believe the new coaching staff and the return of the 4-3 defense will help turn things around. They struggled last year to adapt to the 3-4 scheme implemented by former coordinator Sal Sunseri.

New defensive line coach Steve Stripling, who has over 30 years of coaching experience, joined Jones at Central Michigan in 2009 and followed him to Cincinnati and Tennessee. His teams have averaged 32.3 sacks over the last four years. Tennessee hasn't had more than 26 sacks in a single season since recording 33 in 2005, the last year it ranked in the top half of the SEC in sacks per game.

"If you can't pass rush, you can't be on the field," Walls said. "He teaches it a whole lot, and he preaches it a whole lot. That's where the sense of urgency is. That's the reason we're going to be better."

But their job just got tougher.

Smith has 19 ½ career tackles for loss and has won raves from teammates and coaches for his leadership. Vereen had four sacks in the spring game, and Stripling has called him "one of the highest-motivated young men I've ever seen."

The Vols may need to lean more on junior Jordan Williams, who made five starts last year. Maybe they turn to redshirt freshman LaTroy Lewis, who missed last season with a torn anterior cruciate ligament. Jones said freshman Jaylen Miller has done "a great job" and could contribute.

"We knew from the start we needed to have a lot of intensity and a sense of urgency going into camp to begin with," Lewis said.

That sense of urgency only increases now.