SAN FRANCISCO _ The hits just keep coming for the Carolina Panthers' banged-up offensive line.
The Panthers put starting center Ryan Kalil and his backup Gino Gradkowski on injured reserve Tuesday, further depleting a line that has been depleted by injuries much of the season.
Kalil, who has been dealing with a shoulder injury the past month, will have surgery to repair his right shoulder, a league source said Tuesday.
Kalil missed two games _ including a homecoming game at Los Angeles _ before reinjuring the shoulder in a Nov. 17 win against New Orleans. Kalil, 31, a five-time Pro Bowler, did not make the trip to northern California.
Gradkowski, signed during the offseason as insurance behind Kalil, has been dealing with a knee injury that forced him out of Sunday's loss at Oakland. Tyler Larsen finished the Raiders' game at center.
In a corresponding move Tuesday, the Panthers signed two offensive tackles _ former New England Patriots guard/center Ryan Wendell and offensive tackle Dan France, who was on the Cleveland Browns' practice squad.
Wendell, 30, started 49 games in seven seasons with the Patriots, including the Super Bowl victory against Seattle two seasons ago. Wendell hasn't played since going on injured reserve with a knee injury last November.
France was an undrafted free agent with the Cincinnati Bengals in 2014 and has spent time on practice squads with the Bengals and the Browns. France had never been on an active roster before Tuesday.
Kalil and Gradkowski join left tackle Michael Oher on injured reserve. Oher missed two months while in the concussion protocol before the Panthers placed him on the injured list.
But those aren't all the injuries up front.
Right tackle Daryl Williams sprained his left ankle against the Raiders and is expected to miss at least a week.
The Panthers (4-7) ended the Raiders' game with only one offensive line starter at his customary spot _ left guard Andrew Norwell.
The spate of injuries led Panthers coach Ron Rivera to agree with the premise that the Panthers have reached a "position catastrophe," as they did in 2014 along the offensive line, as well.
"It's about as catastrophe as you can get," Rivera said Monday. "I mean, when you look at the losses we've had this year. But our coaches will coach up the guys that are available to us."
Wendell and France will practice for the first time Wednesday at San Jose State, the Panthers' practice site this week before Sunday's game at Seattle.
Carolina also signed two offensive tackles to its practice squad Tuesday _ former Minnesota Vikings sixth-round pick Tyrus Thompson and Jake Rodgers, the Atlanta Falcons' seventh-round pick in 2015.
Thompson was a teammate of Williams, the Panthers' injured right tackle, at Oklahoma.
