OXNARD, Calif. -- The discussion about Dallas Cowboys linebacker Justin Durant this summer has mostly centered around who or what he isn't.

Durant isn't Sean Lee, the defensive captain and proven playmaker who will miss the entire season due to a torn ACL, prompting the coaches to move Durant from the strong side to middle linebacker.

Durant isn't a former eighth overall pick, like Rolando McClain, the man the Cowboys traded for and talked out of retirement to compete with Durant for the right to replace Lee.

Here's what Durant is: arguably the most productive Dallas defender so far this summer. Perhaps that's damning with faint praise, but Durant has undoubtedly impressed the coaching staff with his performance during training camp.

"With Sean's injury we needed LBs to step up and he certainly is one of them who's taken charge," head coach Jason Garrett said. "One of the examples was on the tape to our team last night of him just running all over this field the last couple days against the Raiders, playing with a relentless spirit and making a lot of plays. He's really showing command and decisiveness playing that spot. He's really had a good camp."

Durant was close to dominant during the second practice against the Raiders. He had a spectacular, leaping deflection on a deep wheel route to Pro Bowl fullback Marcel Reece, another pass breakup on a pass over the middle and several stuffs on running plays.

He looks like he's been playing middle linebacker for years, not months.

"I'm feeling really confident -- confident and comfortable," Durant said. "Like I said, the more reps that I got, the better I was going to feel. Throughout this whole camp, I've just been focusing on the Mike. I think that if you go and look at it, I'm feeling really comfortable with the reads, comfortable with everything that's going on."

That doesn't necessarily mean Durant, a seven-year veteran who was limited to 10 games due to injuries last season, will be the Cowboys' starter at middle linebacker. But it's a good bet that he will start at one of the linebacker spots.

Durant has gotten limited work at the weakside linebacker, which Garrett says might be his most natural position. If McClain plays well in the preseason, the Cowboys could slide Durant over to the Will and bump underachieving Bruce Carter to the bench.

Durant vows to be prepared to do his part, regardless of position.

"I think I really came in with a different mindset to be honest with you," Durant said. "I've always taken it seriously, being my job, but I had a different type of focus coming into this season. ... I just wanted to go out there and show my teammates that I could be the next man up and I'm ready to do whatever I have to do."