The highly-rated 19-year-old joined the German side last June following his first call-up to Japan's senior squad, vowing at the time to become the "new Arjen Robben", Bayern's mercurial Dutch winger.
Despite scoring all five goals in a 5-0 friendly rout of a local side in Qatar last month, Usami has failed to convince Bayern to sign him on a full transfer.
"It's a real pity for Usami but I hope he views it as a valuable experience," Gamba president Kikuo Kanamori told local media. "We would like him to come back [to Gamba]."
Usami, who made three substitute appearances for Bayern's first team, is expected to look for another European club.
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