If HSV rings a bell, it's for good reason: that's where Valon Behrami is plying his trade this season after pouting his way out of Naples in the summer. He's played 16 underwhelming matches in midfield for Hamburg, and his side finds themselves 14th in the Bundesliga and on the ragged edge of the relegation zone. Hamburg aren't in dire need of defensive help as their back line has done well*, but some injuries have left them a little thin.
*Hamburg have given up just 19 goals in 17 league matches, but are so low in the table because they've only scored nine. That's ... bad.
Werder Bremen, on the other hand, have given up the most goals in the league, 39 in 17 matches, and have yet to find a back line alignment that's much better than "shockingly disastrous." While any Napoli fan would tell you that Britos isn't any great shakes himself, it's hard to argue that he wouldn't be worth trying with how poor their other defenders have been.
Napoli are reportedly hesitant at best to let Britos go, preferring to wait to see if one of the German clubs makes a sufficiently large offer. Even though Britos' contract is up at the end of the season, he's needed as depth for now, unless Napoli makes a purchase that gives them an upgrade for their third center back. Of course, a decently large offer would force Napoli to make that purchase and give them a little bit more money to spend on a new defender, so it wouldn't be the worst thing in the world if Hamburg or Werder get desperate.