Like Pulisic, Reyna moved from the US to Dortmund and is now impressing in the first team.
"He must continue to prove himself. We want to see how he does and we are all happy that he is with the national team," said Pulisic.
"With Gio, there are no limits to how far he can go. He has a bright future ahead of him.
"But like I said, he still has a lot to prove before he's there. We see great potential and talent, and we are happy about that."