The 24-year-old's current Bayern deal expires in June 2015 and talks over a new contract have reportedly stalled in recent months.
Manchester United have been strongly linked with the midfielder, but Effenberg has told the German international to 'think carefully' before leaving the Allianz Arena.
"Put it this way - if you have the opportunity to form a successful era at Bayern, you should think two or three times about what step to make," he told Goal.com.
"Every player feels enormously well in Munich and at the end of the season, there are titles. Kroos is a key figure, a transfer shouldn't be an issue.
"He is an important and crucial player - for the system and the new philosophy."
Effenberg initially represented Bayern between 1990 and 1992, before returning for four seasons in 1998.