Many were surprised not to see his name on the US national team January camp roster announced by manager Jurgen Klinsmann on Sunday.

But D.C. United attacker Chris Pontius made sure to use Twitter to clarify why he wasn't among the MLS-heavy list of 25 names that will start training camp on Monday at The Home Depot Center.

Appreciate all the support peeps. Pulled myself out of this camp cause groin isn't 100%. Need to be ready for MLS season — Chris Pontius (@ChrisPontius13) January 6, 2013

The groin injury is the same one that forced Pontius out of the two-leg 2012 Eastern Conference Championship against the Houston Dynamo. He was an early sub in the opening leg at BBVA Compass Stadium in November.

Pontius, who had a career-high 12 goals and four assists for D.C. United during the 2012 regular season, was last called up by Klinsmann in late 2011 ahead of matches against Costa Rica and Belgium. He is still awaiting his first USMNT cap.