So much for Atlanta having to worry about playing time for 3 top cornerbacks, the Falcons lost one of them in their very first game.

Brent Grimes is out for the year after an Achilles tendon injury in a 40-24 win at Kansas City, coach Mike Smith announced.

Grimes left in fourth quarter with what was at 1st called a calf injury. After an MRI, it was determined he is going to need surgery for a torn Achilles, costing Atlanta one of its best coverage players just as the team is beginning preparations to host Peyton Manning and the Broncos in a prime-time game. Vegas odds

It wasn’t immediately clear how Grimes was hurt or maybe which leg he injured.

“Obviously it hurts our depth anytime you lose a player of that caliber,” Smith asserted. “Brent has made numerous huge plays since we have been here. He’s been the cornerstone stone at that corner position, on both the left and right side. We’ve got to have that next-man-up mind-set. That’s how we need to approach it.”

The Falcons appeared to have a wealth of depth at that position after trading for 4-time Pro Bowler Asante Samuel during the offseason. Actually some puzzled how the Falcons would keep everyone happy, since they already had Grimes and Dunta Robinson at the corner spots.

New defensive coordinator Mike Nolan planned to make it work by moving Robinson inside and going with a nickel package most of the time, which was obvious in the 1st game. The Atlanta Falcons started all 3 corners and used their base defense – 2 corners and Akeem Dent at middle linebacker – on just 11 snaps.

Now, the benefit of having 3 top cornerbacks in the pass-happy NFC South is gone.

“We felt like adding a corner gave us 3 number one cornerbacks,” Smith asserted. “Unfortunately, after the 1st game, we’ve had an injury. We’ll need to adjust and we may adjust. Some guys will get an opportunity to play. I know they are anticipating it and I know they’re going to go out and complete.”

But the Falcons have nobody on the bench who can match Grimes’ abilities. He was a Pro Bowler in the 2010 season and got the franchise tag this past offseason when he couldn’t settle on a new contract, receiving a salary of $10.2 million.

Chris Owens appears most likely to step up, but he’s yet to live up to what the Falcons expected after picking him in the 3rd round of the 2009 NFL draft. The only other cornerbacks on the roster are Robert McClain, who is with his 3rd team in 3 years, and Dominique Franks, who was essentially cut by Atlanta during the preseason but was brought back before the opener.

Robinson is more physical in the slot than Franks and Owens, while he has struggled in area coverage on the outside. Grimes made more plays on the ball outside and will likely be missed in the team’s man-to-man coverages.