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.