The thinnest position on D.C. United's depth chart just got thinner, as Steve Goff of the Washington Post has reported that fullback Chris Korb is out for the season with a torn ACL. Korb suffered the injury while trying to shepherd a loose ball out of bounds against New York City FC's Angelino. Given the normal recovery time, Korb's earliest likely return won't come until mid-February at the earliest.
Korb has been a regular despite not necessarily being part of United's best eleven. Only seven players have seen more minutes in league play, and Korb's ability to play both sides of defense would make him a very useful player to have on the bench even when he's not starting.
United already lacks depth at right and left back, with rookie Luke Mishu and Homegrown player Jalen Robinson largely untested at the MLS level. Sean Franklin was always likely to regain his job as the starting right back, but with the CONCACAF Champion League starting up the Black-and-Red will need to do plenty of rotating. Ben Olsen has actually seemed to prefer Steve Birnbaum thanks to Kofi Opare's ability to fill in centrally.
Other options include Nick DeLeon - who has played right back on an emergency basis several times over his career - and perhaps Michael Farfan, who was used as a fullback a few times when playing for the Philadelphia Union (though admittedly following the habits of the Nowak/Hackworth era Union is probably not a good idea). It would not be a surprise at all if United fields Robinson at right back Wednesday night against Arabe Unido, but the most likely replacement for Korb in the matchday 18 - assuming everyone else is healthy - will be Mishu.
United still has a month to make a signing, but the only sort of player they can add would be a free agent. MLS's transfer window is closed, and the trade deadline has passed. The Black-and-Red surely have available fullbacks on a list somewhere at RFK Stadium, but getting an out-of-contract player fit in time to make a contribution - not to mention getting him to fit into United's scheme - would take a month in the best possible scenario. Most likely, a free agent signing might not be able to offer more than the players currently on the roster.