PITTSBURGH -- The Pittsburgh Steelers have invested heavily in the secondary the last few years and still appear to have depth issues.

Their third cornerback this preseason has been a safety, rookie Sean Davis. The Steelers would like to sign Keenan Lewis but have not because of his lingering groin/hip issues.

But with 15 days before the opener at Washington, the Steelers are experimenting with lineup changes in practice.

On Sunday, the team worked this group together, according to defensive coordinator Keith Butler: veteran William Gay in the slot, safety Robert Golden moving to inside linebacker (which he did at times last year in the nickel package), Davis at safety alongside Mike Mitchell and first-rounder Artie Burns on the outside alongside Ross Cockrell.

Burns was back at practice Sunday after missing much of the last month with a quad injury.

"We are going to look at other things," Butler said. "We take a look at that to get a feel for where they are at."

Asked about whether corner depth is a concern -- the fourth corner is anyone's guess -- Butler said, "We've got some guys who could end up being pretty good players."

This lineup would get the Steelers' top two picks, Burns and Davis, on the field together. Davis has split time between safety and slot corner.

If Burns is ready for game action, he gives the Steelers more flexibility. He's a true outside corner. And he's expected to play a lot in the final preseason game so the Steelers can evaluate his readiness.

"He needs to play and he looks like he's fine to me," Butler said. "He looks like he's ready to play. He's behind in regards to being on the field. You can't substitute for that."

Generally, Butler likes what he's seeing from all of his defensive rookie draft picks, particularly third-round tackle Javon Hargrave. The Steelers felt they were getting a 'steal' in Hargrave during April's draft, Butler said, and Hargrave has affirmed that belief.

As for Davis, the Steelers like him enough to try him at both spots. Butler said he's making sure not to overload him and admits certain slot receiver matchups have been a challenge for the rookie. For example, Lions receiver Anquan Bolden "schooled him a little bit" in the preseason opener, Butler said.

"He can handle it mentally," said Butler of Davis playing both spots. "Physically, we'll see."

Butler is trying to get his group game-ready for the Washington Redskins now. After Sunday's practice, Butler personally ran a group of linebackers and defensive backs through a handful of 'suicide' sprints because, as he says, the game tackling needs to improve.

"Their legs are tired right now," Butler said. "I'm going to make them more tired, make sure their legs are Ok before we play that Monday night game."