In September 2022, which of the following tennis players announced his…

Current-affairs "who announced X" questions are resolved by matching three anchors at once: the exact month, the reason stated in the athlete's own announcement, and the specific event tied to it — not by general familiarity with a player's career timeline.

Roger Federer announced on 15 September 2022, in a video message, that he would retire from professional tennis after the Laver Cup (23-25 September 2022). His announcement pointed to the cumulative toll of injuries, multiple surgeries, and rehabilitation attempts on his body; he and subsequent reporting made clear this centred on his right knee, which had not recovered from surgery as he had hoped despite repeated procedures — matching the stem's month, reason, and body part.

• Novak Djokovic remained an active tour player in September 2022; that period he was barred from entering the United States for the US Open under COVID-19 vaccination-based travel restrictions, not because of a knee-related retirement.

• Rafael Nadal also continued competing in September 2022; his significant 2022 injury news concerned a chronic left-foot condition and a separate abdominal-muscle tear, and he did not retire until 2024.

• Andy Murray had hip-resurfacing surgery in 2019 and kept playing professionally well past September 2022, with no right-knee retirement announcement that month.

So among the four, only Roger Federer's own September 2022 statement ties a retirement decision to recovery from right-knee surgery — the answer is Roger Federer.