It's now or never for John McCargo.

The Buffalo Bills have been waiting for the veteran defensive end to blossom into an impact player. But time is running out on the fifth-year veteran, who is fighting to win a roster spot in what might be his final season with the team that drafted him in 2006.

No one has to tell him what is at stake this summer. He already knows.

"I definitely do," said McCargo, who is entering the final year of his contract. "I have a lot to prove. That's what I'm trying to do out here."

McCargo's career has been hindered by injuries and inconsistency since the Bills made a surprising move to trade up into in the latter part of the first round to draft him with the 26th overall selection.

In his rookie year, he was limited to five games by a foot injury, but he showed real promise during his second year with 45 tackles and 2.5 sacks. It was the first and only time he has appeared in all 16 games in a single season.

In 2008, he fell out of favor with former defensive line coach Bill Kollar and barely got on the field. The Bills tried to trade McCargo to Indianapolis midway through that season, but the Colts nixed the deal when he failed a physical because of a bulging disk in his back, which ultimately led to the Bills putting him on the injured reserve list.

Things weren't much better last season for McCargo, who accounted for only 10 tackles and missed five games with a calf injury.

"Once you get in a rut, no matter what you do you've got to work yourself out of that rut," McCargo said. "I've been in a rut for a while just because of injuries and other things with me mentally. But I'm just trying to get back on track. I'm healthy, which is number one. I'm just hoping that somebody will notice that I'm trying to play football and give me a chance to play."

It looks like new head coach Chan Gailey is giving McCargo a chance to redeem himself in what is clearly a make-or-break year.

So how is he doing?

"I tell you what, he has done a really good job so far," Gailey said. "He's making it more than he's breaking it."

Despite what Gailey says, McCargo is not a lock to make the regular-season roster. He ran with the third-team defense for most of training camp, though he did get a few snaps with the ones and twos. The top four D-ends are set with starters Dwan Edwards and Marcus Stroud backed up by Spencer Johnson and rookie Alex Carrington, a third-round pick.

McCargo would be the odd man out unless the Bills kept five ends, which is possible but far from certain. It would help his cause if he is able to master his new position in the Bills' new 3-4 defense.

The scheme appears to be ill-suited for a player who is a natural "three-technique" defensive tackle in a 4-3. But McCargo believes the transition to defensive end is going well.

"It's different from what I'm used to, but I feel like I'm getting it," he said. "It starts with the hands, using good hand technique in the two-gapping scheme. On this level, everybody is athletic. But you've got to be able to know where to go. When you've got to contain, you've got to get contain. When you've got the B-gap, you've got to be accountable for that gap. So it's definitely more mentally challenging because we've got a lot more plays and a lot more movement up front.

"But at the end of the day, it's just football. It's about going out there and competing and beating the man in front of you."

McCargo's first two preseason games were a mixed bag. He accounted for three tackles, including two behind the line of scrimmage, and a sack in the opener at Washington. But he was barely visible in the Bills' win over the Colts last Thursday.

There are two more games left in preseason, time enough for McCargo to earn a roster spot and take another step towards turning his career around.

"The coaches have given me an opportunity to go out and make some plays," he said. "I just have to take advantage of them."

awilson@buffnews.comnull