Arsenal loaned out Reiss Nelson because he needs “a new level” and “to take minutes”.
Nelson joined Hoffenheim on a season-long loan ahead of the European transfer deadline this week.
The 18-year-old made an impressive 16 appearances for Arsenal last season, eight of which came in the Europa League.
But he has been shipped out on loan by Emery, who is eager for the youngster to build his “experience” elsewhere.
“It’s a very big chance for him and the level there is important,” he said.
“We think he needs, because he is very young, he needs to take a new level to play, a new level also to take minutes, to take experience and it’s for that reason we were speaking at the club with the coaches about this possibility.
“And also, with him, we decided together: club, coaches and the player. It’s a good chance for him to take minutes in and play, and then come back with us because I think he is signing a new contract with us.”