David Ruiz of Univision is saying that D.C. United defender Steve Birnbaum is on the watchlist of Bundesliga side Borussia Dortmund. It does not say that there is an offer for the 25-year old defender, but it does say that sporting director Michael Zorc is looking to fill the position left by Mats Hummels, who will be leaving Dortmund this summer to join Bayern Munich.
This would not be the first team interested in Birnbaum, as Steve Goff reported that Israeli side Maccabi Haifa was interested in his services, but it would be a side with a big international profile. Aside from being in one of the world's top leagues, Dortmund will have UEFA Champions League play next season. If this rumor became an actual transfer, Birnbaum would join Christian Pulisic as part of Die Borussen. Along with whatever fee would be collected in the transfer, United has in the past shown an interest in pushing for a sell-on clause (where D.C. earns a portion of the funds from whatever transfer happens afterwards) as part of the deal.
The closer we get to the summer, the European interest in Birdbomb (with World Cup qualifiers under his belt and a presumable Copa America roster spot with his name on it), will be at its highest thus far. Expect to hear a plethora of rumors along these lines from now until the summer window closes.