For years, fans admired Mark Harmon’s strong and steady presence on NCIS, never imagining he was quietly dealing with serious health concerns behind the scenes. According to close sources, Harmon faced a significant health scare that he managed to keep under wraps while continuing to film the hit series. Around 2016, he underwent a major knee surgery due to lingering damage from his college football days — an injury that had worsened over time.

The surgery took a toll. Harmon lost a noticeable amount of weight during recovery, prompting concerns from fans who saw changes in his appearance on screen. But what no one knew was how intense his rehab process truly was. Behind the scenes, Harmon pushed through pain and physical therapy with intense dedication, even incorporating Pilates into his routine — a practice he admitted was far more challenging than expected.

Despite the physical setbacks, he remained committed to his role as Leroy Jethro Gibbs, refusing to let the cast or audience sense any weakness. Many now look back on his final seasons with new respect, knowing he was balancing immense physical strain with a demanding filming schedule. His quiet strength, both on and off screen, continues to inspire.