Alex Knaff (born 26 November 1997) is a Luxembourgish tennis player. Knaff has a career high ATP singles ranking of 597 achieved on 07 November 2022. He also has a career high ATP doubles ranking of 435 achieved on 26 September 2022. Knaff represents Luxembourg at the Davis Cup since 2015, where he has a W/L record of 10–9. Knaff played college tennis at Florida State University.