If Hardwick needs the full rehab period, he could miss the early part of the regular season.
Hardwick was hurt early in a game against the Oakland Raiders on Oct. 14 and missed the next four games. He played in the final six regular-season games and three playoff games.
Hardwick had surgery on March 14 but the team didn't announce it until Wednesday.
On Feb. 28, the Chargers released a list of 11 players who either had surgery since the season ended or had surgeries planned. Hardwick's name wasn't on the list.