The Cowboys handed out nine figures' worth of contracts in free agency this offseason but didn’t address their biggest offensive weakness.

Phil Costa will still be the starting center when the Cowboys report to training camp. His competition: 2011 seventh-rounder Bill Nagy, who played guard before suffering a season-ending broken ankle in the fourth game last season; and second-year undrafted free agent Kevin Kowalski, who missed offseason workouts because of a foot injury.

There was some thought about free-agent addition Mackenzy Bernadeau playing center, but that was tabled after his hip surgery. The Cowboys plan for Bernadeau to focus solely on guard when he’s ready to begin practicing, perhaps midway through training camp.

The Cowboys thought Costa, who joined the team as an undrafted free agent in 2010, was ready to be a starter when they cut overweight, overpaid Andre Gurode last summer. They thought wrong.

According to ProFootballFocus.com’s grades, Costa ranked 30th among centers last season. There were only three centers who had worse grades in pass protection.

“Absolutely he has to do things physically better and he has to do things mentally better and emotionally better and all those things,” Cowboys coach Jason Garrett said. “He’s working very hard at that. Certainly the experience will help him. The fact that he was a starter and played all those snaps for us last year will help him. But he has the right approach.”

You can’t question Costa’s work ethic. Garrett loves his “bulldog mentality,” and Costa probably spends more time lifting weights and watching film than he does sleeping.

But Costa has physical limitations that won’t change. His short arms -- the primary reason he didn’t get drafted -- aren’t going to grow. It’s tough not to get overpowered in NFL trenches if you can’t get your hands on the man you’re battling.

Costa’s work last season provided plenty of examples of that. The most glaring was probably when blitzing linebacker Brandon Spikes planted Costa on his butt a few yards deep in the backfield on the first play of the three-and-out series in New England that preceded the Patriots’ game-winning drive.

There aren’t many plays that work when the center gets driven backwards.

Maybe the Cowboys can give Costa more help after signing Nate Livings, who was inconsistent for the Bengals, to start at left guard. But the interior line was the offense's biggest issue while finishing middle of the pack in points scored last season, and that hasn't changed.