Julian Green would have played for the United States under-23 squad in Wednesday's friendly against Mexico, but new Hamburg coach Bruno Labbadia gave permission hours too late, according to U.S. assistant coach Andi Herzog.

The 19-year-old Green, who scored in the Americans' 2-1 loss to Belgium in the World Cup round of 16 last summer, traveled from Germany to Texas last week but didn't play in the U.S. senior team's 2-0 win over Mexico in San Antonio.

Herzog, who serves as head coach of the U.S. U23s, wanted Green to stay on for Wednesday's JV match in Carson, California, and made the request to Hamburg sporting director Dietmar Beiersdorfer, his former teammate at Bundesliga club Werder Bremen in the 1990s.

"He said he had to talk to the coach," Herzog, whose team will attempt of qualify for the 2016 Olympics later this year, told ESPN FC.

The U.S. did not receive permission for Julian Green to stay with the under-23s until it was too late. AP Images

But by the time Labbadia, who became Hamburg's fourth manager this season on April 15, gave his blessing, Green was already on his way back to Germany.

"I was waiting for his answer when Julian left," Herzog said. "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."

Green, on a season-long loan from Bundesliga leader Bayern Munich, has found playing time scarce at HSV. He's seen just 113 minutes of action in his five league appearances, the last of which came in November. In February, he had a public falling out with the club over his demotion to its reserve side.

Herzog hopes that Green will get a fresh start under Labbadia.

"Hamburg is in big trouble," the former Austria U-21 boss said of the last place club. "If Julian is doing well in training, maybe he gets a new chance now."