Answer
Marcell Jansen began his professional career with Borussia Mönchengladbach, a German football club based in Mönchengladbach, North Rhine-Westphalia. He joined the club's youth academy in 1997 and made his senior debut in 2004. Jansen went on to make over 100 appearances for Borussia Mönchengladbach before moving to Bayern Munich in 2007.