Bremen had an largely forgettable German Bundesliga campaign last term, briefly flirting with relegation before finishing in 13th.
The club's onfield woes have seen many suggest that key players could be unhappy with the lack of progress and soon seek a move elsewhere.
Marin has reportedly long been courted by a host of top European sides including Liverpool and Tottenham, while goalkeeper Tim Wiese is said to be being monitored by Wolfsburg, who are eyeing a replacement for Swiss custodian Diego Benaglio, whose future at the club remains uncertain..
However, Bremen sporting director Klaus Allofs has since consigned these rumours as pure fabrication, before suggesting the club were themselves on the lookout for defensive reinforcements.
"We are continuing our chase and hope for a quick solution," Allofs told Sportal.
Marin himself has recently come out declaring his commitment to the club, telling Bild: "I have no interest in such speculation."
According to L'Equipe, Bremen coach Felix Magath is preparing a €12million bid for Lyon's out-of-favour midfielder Miralem Pjanic, who was consigned to a reserve role last season.