With cornerback Brent Grimes out for the year, Falcons coach Mike Smith said he and his coaches will have to re-configure their nickel coverage. (AP Images)

The mood in Atlanta quickly turned grim following its 40-24 victory over Kansas City as news of CB Brent Grimes’ torn Achilles spread. An MRI revealed that Grimes will need surgery and the Falcons have placed the 2010-Pro Bowler on injured reserve. It’s especially bad news for the fifth-year defensive back because this is the final year of his contract.

Fortunately for Atlanta, the secondary was the one unit upgraded through offseason acquisitions. Asante Samuel, the team’s lone free agent still with the team, started at left cornerback on Sunday and Grimes’ injury will push veteran Dunta Robinson outside on the right. The biggest impact will be felt in nickel coverage, since coach Mike Smith felt Grimes, Samuel and Robinson were all starting-caliber corners.   

The most likely candidates to fill Grimes’ role will be Christopher Owens, who had 35 tackles in 14 games last season or Dominique Franks, who was signed last week after getting released during training camp. Despite Franks’ whirlwind preseason, he’s still a viable candidate to help the defense. He played 14 games last year with 15 tackles.

“I think that’s probably the biggest thing we have to do is figure how we want to configure who’s going to be playing in our nickel package,” Smith said on Monday. 

Kansas City’s Matt Cassel picked apart the Falcons’ secondary in the first half, which often seemed content to play soft zone coverage. Cassel completed 11 passes in the first half for 123 yards and a touchdown. He scrambled five yards in the second quarter for another score to tie the game at 17. Defensive coordinator Mike Nolan increased the pressure on Cassel in the second half and the Falcons' defense kept the Chiefs out of the end zone and recorded two interceptions. 

The secondary figures to get a huge test Monday night when the Falcons host the Denver Broncos.  Peyton Manning   will undoubtedly pick on the cornerback in Grimes' old spot. Communication will be paramount, as Manning will speed the game up operating the no-huddle offense. 

“It didn’t look like their quarterback had missed a whole lot of time,” Smith said of Manning, who made his return after missing all of 2011 following neck surgery. “Peyton Manning has probably done [a no-huddle] better than anybody in the history of the NFL for years and years with the Indianapolis Colts.” 

For more Falcons coverage, follow Mike Singer @CBSFalcons.