Simon Cowell is absent from America's Got Talent season 21 live episodes whilst recovering from routine back surgery undertaken in August. His fellow judges—Sofia Vergara, Howie Mandel and Mel B—have publicly acknowledged how significantly his absence is felt on the panel, with Mandel comparing the situation to "sailing without the captain." Despite the challenge, the judges have maintained that the show must continue, with the production bringing in guest judges to fill the vacant seat.

Cowell's surgery addressed injuries sustained in a 2020 electric-bike accident, and his representatives indicated he would return after several weeks. To maintain the panel, the show has rotated guest judges including comedian Kenan Thompson and former judge Heidi Klum, who returned for the 8 September episode after departing following the 2024 season. Klum's temporary return has proved seamless, with the judges praising her chemistry with the team, whilst British social media personality KSI will join the panel for the season 21 finale.