Per the NFL Network's Rand Getlin, the Panthers have signed offensive lineman Fernando Velasco. His name should ring a bell, as he started 7 games for the Panthers last year and filled in for a then-rookie Trai Turner, who was coming off an injury to start the season. This is likely a move to give the Panthers another option at center more so than guard as Ryan Kalil continues to play through injury.
If you've been keeping an eye on the transaction list, you'll see a concerted effort to find a backup plan for Ryan Kalil. The team didn't want him to play all of week one but that ended up being the case when rookie offensive tackle Daryl Williams went down with a multi week injury on his first snap of the season.