Patriots have depth concerns on offensive line

The returns of Logan Mankins (ACL) and Brian Waters (hasn't reported) are anticipated at some point, but they probably can't come soon enough.

The performance of the Patriots' guards and centers has not been good so far in camp, and the depth took another hit on Sunday when reserve Jamey Richard left with what a league source said was a concussion.

Starters Dan Koppen (center) and Dan Connolly (guard) struggled mightily in one-on-one drills. Koppen is more of a concern than Connolly, who was solid the previous day.

But the Patriots are going to need to improve their depth. Don't be surprised if they start signing a few more players.

Follow Patriots reporter Greg Bedard on Twitter: @CBSSportsNFLNE.