In 1992, Stumpf joined Galatasaray and went on to win the double of Süper Lig title and Turkish Cup in 1993.

Back in Germany, he joined Hannover 96’s minor league team in 1997 before ending his active professional career here.

After Rehhagel's resignation in October 2000, Stumpf became head coach, Andreas Brehme taking over as the Red Devils team manager.

The duo's last stop was a two-year stint with renowned Turkish club Galatasaray, winning the 2005–06 Super Lig.

In August 2009, he once again became assistant coach under Erik Gerets, this time at Al-Hilal in the Saudi Professional League.

In September 2011 he signed a contract as head coach at Tunisian side Club Sportif Sfaxien.

On 29 December 2011, Sfaxien released Stumpf due to the German's inability to communicate adequately with his underperforming players.