Steelers can't afford injuries to secondary

The Pittsburgh Steelers announced that cornerback Cortez Allen underwent minor surgery on his right knee Friday.

When it comes to the Steelers' secondary, nothing is "minor." It's a concern.

Coach Mike Tomlin estimated that Allen would be back on the field in a couple of weeks. This could mean missing only a couple of preseason games, which is not a big deal when you hear about the serious injuries happening at training camps around the league. But any injury to a Steelers cornerback is a reminder to how little depth Pittsburgh has at one of the most critical positions in the game.

Allen, a 2011 fourth-round pick, is expected to replace Keenan Lewis, who signed with the New Orleans Saints in free agency. With Allen sidelined, William Gay will move back into the starting lineup, which shows how dire the Steelers are at cornerback. Gay has familiarity with the Steelers system (he started 15 games for Pittsburgh in 2011), but he's not a starting caliber defender. Last season in Arizona, Gay was the 105th-rated cornerback by Pro Football Focus.

So, why would the Steelers sign Gay? Pittsburgh didn't have much faith in Curtis Brown, who struggled last season, to be the team's No. 3 cornerback. The Steelers also couldn't afford much better than Gay because of their salary-cap situation. According to The Pittsburgh Post-Gazette, the Steelers will likely use rookie safety Shamarko Thomas as the nickelback while Allen is sidelined instead of going with Brown.

Last season, the Steelers finished with the top-ranked pass defense in the NFL. If the Steelers suffer a more serious injury at cornerback, pass defense could become a major weak spot.