A former mainstay at Freiburg before making a move to England with the Bees in 2023, Flekken previously gained plenty of playing experience in Germany after joining the Alemannia Aachen youth set-up as a 16-year-old. Spells at Greuther Fürth and Duisburg followed for the 6'4" custodian, before Freiburg came calling in 2018.
Amassing 80 Bundesliga appearances and 26 shut-outs across five seasons at Freiburg, Flekken was part of the Christian Streich-led side that qualified for the UEFA Europa League and enjoyed a run to the 2022 DFB Cup final.
"Mark exudes an impressive physical presence, and in footballing terms he has certainly been one of the best keepers in the Premier League over the past two years," said Leverkusen sporting director Simon Rolfes. "He knows the Bundesliga from his successful time in Freiburg. His years in England and his role in the Dutch national team have also given Mark a great deal of international experience."
