Aleksandar Bajin (born 4 October 1984) is a German tennis coach and former player of Serbian origin. He is best known for coaching Naomi Osaka to two Grand Slam titles at the 2018 US Open and the 2019 Australian Open. He won the inaugural WTA Coach of the Year award in 2018 for coaching Osaka to her first two titles at the US Open and the Indian Wells Open. Bajin and Osaka split shortly after her Australian Open title. In April 2019, he began working with Kristina Mladenovic. He split with her in October 2019 and started coaching Dayana Yastremska.
Bajin had previously served as a hitting partner for Serena Williams for eight years, and held the same role for Victoria Azarenka, Sloane Stephens, and Caroline Wozniacki. Bajin had a brief career on the Association of Tennis Professionals (ATP) Tour, reaching career high rankings of 1149 in singles and 1180 in doubles.