The Germany defender is being linked with Arsenal and Tottenham.
He told BILD: "You have to be going back to aspects like gratitude, respect and affinity. You have to keep in mind what a club has done for yourself over years, you should never forget that.
"Players moving clubs fast and often is a behaviour I deplore, I hate that.
"At the moment I am extremely keen to prevent any scenario of people being able to say I am a mercenary, only thinking about money.
"I am not going to say I would not be able to deal with not playing in a European Cup competition next season.
"You are able to deal with any situation. You have to keep promises you made, even if they were made years ago.
"The situation at Werder Bremen is extremely precarious. I am certainly not going to monitor my feelings (about leaving), I am not going to make any statement on myself as long as the club is in such a situation - a situation which the club was put in by the players."