Background
Grassow was born and raised in Berlin, before moving to Munich the age of 16.
Grassow was born and raised in Berlin, before moving to Munich the age of 16.
He joined Turn- und Sportverein 1860 München, where he made one appearance in the Bayernliga, before moving on to SpVgg Starnberg and later Football Club Starnberg. He began his senior career in 1993 with SpVgg Unterhaching, where he had four successful years, which earned him a move to Football Club Bayern Munich. After half a season he moved again, joining 1.
Football Club Köln, where his arrival bolstered a struggling defence.
He remained in Cologne for eighteen months, but the club was relegated at the end of the 1998-1999 season, and he left, rejoining Unterhaching, who had since been promoted to the Bundesliga. The club spent two years in the Bundesliga, finishing 10th in their first season, but then suffered two consecutive relegations, falling to the third-tier Regionalliga in 2002.
Grassow stayed with the club as they returned to the 2. Bundesliga, and consolidated their position, before leaving at the end of the 2003-2004 season.
Grassow returned to the Regionalliga, playing for SV Darmstadt 98 for two years, before moving on to Bayernliga side SSV Jahn Regensburg in 2006.
Here he was appointed captain by the coach Günter Güttler, as the side were promoted to the Regionalliga, which they followed with qualification for the new 3. Liga. After one season at this level, Grassow retired.