Hardwick, 33, dealt with a neck stinger during the second half of the 2013 season. He contemplated retirement during the offseason.
Hardwick is in the final year of a three-year, $13.5 million contract that pays him $4 million in 2014. Hardwick's neck injury is potentially career-threatening, and he is not certain to return in 2015.
He anchored an offense line that served as one of the strengths of the Chargers in 2013, and is the only offensive lineman who played in all 16 regular-season games for San Diego last season.
Hardwick left San Diego's season opener at Arizona with a reported left ankle injury and did not return. Hardwick was replaced by Rich Orhnberger, who likely will start against the Seattle Seahawks on Sunday. However, rookie third-round draft choice Chris Watt also spent time at center during training camp.
An 11-year veteran, Hardwick went to the Pro Bowl in 2006.