CHICAGO (AP) - The long-anticipated debut of Jared Allen with the Chicago Bears might be pushed back a week.

The grand unveiling of the rebuilt defense figures to come at a later date, too.Chicago hosts the Philadelphia Eagles on Friday in a preseason opener that still could provide a glimpse even if it's lacking some star power.Allen missed practices this week with his wife giving birth to the couple's second daughter, throwing his status for this game into doubt.If he does play, it will probably only be a cameo since starters generally make early exits.Tight end Martellus Bennett might also miss this one after being suspended indefinitely following an altercation with cornerback Kyle Fuller in practice on Monday.As for the Bears' new-look defense?Well, Friday's game could provide a hint or two of things to come whether Allen plays or not and some position battles could start to come into focus.Throw in the fact that the Bears will face the defending NFC East champions, a team that beat them last season, and there is at least some intrigue in this game. That starts with the defense."We do a few things that are different but the mentality is still there," Bears linebacker Lance Briggs said. "Things that we've always been taught and that's play physical, run to the ball and create takeaways."All those are things the Bears did not do last season on the way to an 8-8 record. Now, they're looking for more on defense, and the same goes for the Eagles.Where they differ is how they tried to achieve it.While the Bears went the makeover route, most notably signing Allen from Minnesota, the Eagles made few changes to a defense that was the worst in franchise history in yards allowed. The 6,304 yards Philly gave up were 15th-most in NFL history and the 4,636 passing yards were fifth-most.The major additions the Eagles made were safety Malcolm Jenkins, cornerback Nolan Carroll and rookie linebacker Marcus Smith, a first-round draft pick. They're also counting on improvement from within to support a record-setting offense as they enter their second season under defensive coordinator Billy Davis."It's really a chance to get to see guys in live action with officials in a different setting and see which guys can show up a little bit," coach Chip Kelly said."And that's the interesting thing of this, there's going to be some guys that I think maybe someone didn't have an idea where they were going to be, and there's going to be some other guys that maybe will disappoint. But you don't know until you can put them into action."