Green, 19, was on the bench for Coach Jurgen Klinsmann’s squad for its 2-0 friendly win over Mexico April 15 in San Antonio.
Labbadia was named head coach of last-place HSV on April 15. Herzog had requested Green’s release from Hamburg sporting director Dietmar Beiersdorfer, but by the time Labbadia signed off, Green was on the way back to Germany.
"He said he had to talk to the coach," Herzog said. "I was waiting for his answer when Julian left. He got back to me five to seven hours later and he said it was fine to have Julian stay, but it was too late."
It’s the latest disappointment in a rough year for Green, who after scoring the consolation goal in the USA’s 2-1 loss to Belgium at the World Cup was loaned by Bayern Munich to HSV, where he’s seen only 108 minutes of first-team action. His last Bundesliga appearance came with a 15-minute stint off the bench in November.
Herzog, who's preparing the U-23s for 2016 Olympic qualifying, said he's hoping the coaching change at HSV will benefit Green.