Alex Knaff (born 26 November 1997) is a Luxembourgish tennis player.
Knaff has a career high ATP singles ranking of 486 achieved on 11 September 2023.
He also has a career high ATP doubles ranking of 364 achieved on 11 September 2023.
Knaff represents Luxembourg at the Davis Cup since 2015, where he has a W/L record of 12–10.
Knaff played college tennis at Florida State University.