Nagatomo to return to Japan for tests
Nagatomo suffered the injury to his right shoulder in a friendly against Scottish side Celtic in Dublin on Saturday, ruling him out of Japan's August 10 friendly against South Korea.
Inter could also miss the full-back for the start of the Serie A season if the injury is serious but Japan coach Alberto Zaccheroni confessed he was worried.
"I don't know how bad it is or how long it will take for him to recover," the Italian told Japanese media, mindful of the third round of 2014 World Cup qualifiers beginning next month.
"I'm praying it's not too serious."
Nagatomo has already undergone tests in Italy after suffering the blow in Inter's 2-0 pre-season win over Celtic.
Japan take on North Korea at home in the third round of World Cup qualifiers on Sept. 2 in their opening Group C game.