The Houston Texans have uncertainty at linebacker. But they also have flexibility and time.

Two things are certain: Brian Cushing will be back from a torn ACL and manning the weak inside spot, and second-year man Whitney Mercilus will graduate to the starter on the weak side.

Two things are uncertain: Who mans the inside spot next to Cushing, and who will line up on the strong side?

There are two primary scenarios.

• One of the team’s rookie outside linebackers, Sam Montgomery or Trevardo Williams, shows up big from the beginning and starts on the strong side, nudging Brooks Reed to the inside.

• One of the team’s injury-prone inside options, Darryl Sharpton or Tim Dobbins, earns the spot alongside Cushing, allowing Reed to remain on the strong side.

Either scenario could be fine on a defense looking to replace Connor Barwin, the weakside linebacker who had a disappointing 2012 and left for Philadelphia as a free agent, and needing to find the right guy to play inside with Cushing.

"The one thing I've learned about Wade Phillips is he knows exactly what he's doing when he drafts a player," Cushing said. "He sees things in people and prospects other coaches and scouts don't. He will always play the best players and we have a lot to pick from now."

Reed can key a lot of the flexibility.

“Brooks can do it [inside], he played inside some last year and he played real well,” said Phillips, Houston's defensive coordinator. “It’s not something foreign. He’s played inside enough where we can say, ‘Wow, he can play inside, too.’ And we’d still rush him on third downs outside. You’d still get the rush factor with him. It’s a possibility.

“But right now, we’re just looking at those two rookies to see how they do. It just depends on how good our young players are, and what they can do.”

Sharpton isn’t part of the Texans' organized team activities right now, still recovering from a hip issue that landed him on injured reserve at the end of the regular season.

For Montgomery and Williams, who were 4-3 defensive ends at LSU and UConn, respectively, the big transition might be about dropping into coverage.

That’s nowhere near as complicated as some people make it out to be, Phillips said. The Texans' defense can drop the strongside linebacker into the flat, but “he doesn’t ever cover the tight end,” Phillips said.

“It’s not that big a deal,” Phillips said. “I think people can go overboard on what kind of drop guy you have to have, because he doesn’t drop all that much.”

Rushing the passer remains the primary job, and the defense rushes five players almost all the time -- typically three linemen and both outside backers.

“This is what we normally get, guys who played defensive end in college," Phillips said. “We’re excited about both of them, we think both of them can do it. I’ve had a lot of them in the past who’ve done it, and these guys both have the ability. We’ll see what happens. Both of them can rush the passer No. 1, and that’s what we look for in outside backers.”

Phillips and the Texans want to have three outside linebackers they can rotate. But in 2011 they lost Mario Williams early, and Barwin and Reed played virtually all the time. Last season, Mercilus wasn’t ready to contribute early, then Reed missed four games because of injury.

If both Montgomery and Williams pan out, and both Sharpton and Dobbins stay healthy, the Texans could have serious depth and actually be able to rotate more on the outside.

But Phillips won’t set any playing-time goals. He said it depends on how good guys are, and what kind of stamina they have. He’s had starters who have played 94 percent and guys who have played 80.

Cushing was lost when he tore up his knee in the Texans' fifth game last season. He looks very good now, Phillips said, and Houston expects him to be on the field on opening day with no issues.

That will be the biggest, and best, change to the linebacking corps.

“He’s running around, he’s running fast and moving well right now," Phillips said. "So I think three months from now he’ll really be ready to go. … He’s a fantastic player, he’s a difference-maker.”

“The type of energy that he brings out there,” Mercilus said of Cushing, “it’s unreal.”

Even without Cushing, and with eight players starting at linebacker at some point, the Texans were seventh against the run in 2012.

Owner Bob McNair said after the season that the team needed better linebacker depth, but it’s silly to think any team can have better depth than the Texans did. Any team needing to play that many guys at one position will have problems.

Moving forward, with defensive tackle J.J. Watt, Cushing and safety Ed Reed, the Texans' defense will be strong up the middle with star players. That is the reigning defensive player of the year in front of Cushing, and a future Hall of Famer behind him.

The team’s 2012 first-round pick, Mercilus, will take over Barwin’s spot, and expectations are high for his second season. He got on the field more late last season when Brooks Reed was hurt and had a bigger role once Reed returned from his groin injury.

Mercilus had six sacks, the third most on a team that relied heavily on Watt, who notched 20.5.

“In Year 2 I can do a lot more, especially coming into a starting role,” Mercilus said. “Run techniques are something I’ll be focusing on a lot more so that I’m a more well-balanced player than I was last year.”

“The position they put me at plays a lot to my strengths. I’m pretty good at rushing the passer, getting after the quarterback. There’s not really a whole lot of thinking, it’s just getting out there and playing ball.”