The Bundesliga club side has shown interest in signing the Nigerian star since last year.
Kalu currently plays for Bordeaux and has not been very impressive since he joined the club side. It is suspected that Real Betis who showed interest last year might also be interested in making an offer for the Nigerian star.
The former Gent of Belgium winger was also left out of the team’s training session yesterday as the rumour with transfer continue to intensify.
Bordeaux boss Paulo Sousa did not look to field Kalu for the team’s last two games against Pau in the Cup and Nantes in the league.
It has been said that Kalu’s position might even be at greater risk with the arrival of Aurélien Tchouaméni and Raoul Bellanova.