The defender, with just over 18 months on his contract, is being linked with a move away, where Liverpool and Atletico Madrid have been mentioned as potential destinations.
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BVB chief Lars Ricksen says they won't pressure Schlotterbeck over contract talks, though Sammer disagrees.
Sammer acts as a consultant to BVB and told Sky Deutschland: "With Nico Schlotterbeck, the most important thing is to understand how far along the talks are.
"I've always looked at it from a sporting perspective. That's why I've often told the club in the past: I know you want harmony and want to give him more time.
"You can do that, but I wouldn't. Sometimes you have to set deadlines."