The 21-year old winger, who left DC for Belgian club Anderlecht in 2012, returned to the RFK Stadium with Honduras for a pre-World Cup friendly with Turkey.
Although Los Catrachos lost 2-0, Najar admitted his delight at being back at the place where his burgeoning career began when he was just a teenager.
"I'm happy to be back," Najar told MLSsoccer.com.
"Honestly, I barely have words. This was the place that I learned to really play at, and those lessons have helped me tremendously in Europe.
"To think that I've gone from [MLS] to Europe and that now I'll be wearing my country's jersey in the World Cup; I'm just so thankful for everything and just want to show well in Brazil."
A grateful Najar added: "I will always remember D.C. United.
"They took a chance on me and I will never forget that; I will never forget the fans or the team, you always remember your first club. I guess it's pretty impressive as young as I am, that within four or five years I've been able to achieve all of this.
"Honestly, like I said, I have no words. I can't complain about anything. I'm just grateful for all of this."
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