Franck Ribery could pose more a problem than a solution for his club Bayern Munich with his want-away attitude, according to former team-mate Oliver Kahn.
"Ribery is not without danger for the club," the former Germany goalkeeper told the daily newspaper.
"A player who constantly plays with the idea of leaving for Real Madrid, Barca or elsewhere, always makes things more nervous.
"You have to seriously consider this issue, otherwise a player becomes more a problem than a solution for a club."
Kahn, who played with Ribery during his final season as a player in 2007-8, said the former Marseille striker, a potential target of Real, Barca and Manchester United, must change his behaviour.
"Bayern have given him the chance by recruiting him to become one of the best players in Europe."
Ribery is under contract with Bayern until 2011, and the club's management have been keen to stress that he is not for sale.