Metin Mert (born Detlef Müller; 21 May 1965) is a German-born naturalised Turkish professional footballer who played as a goalkeeper.

Detlef Müller was born Duisburg, West Germany.

His first Oberliga game for Bochum II was on 31 December 1983 in a 3–0 win against Hammer SpVg.

During a vacation to Turkey in 1988 Müller was spotted by Erdal Keser playing Beach soccer.

He was offered a contract from Sarıyer out of the Turkish First Football League, which he accepted.