Hosogai set to join Leverkusen
"I made a positive decision to put myself in an environment that will be tough for me," Hosogai was quoted as saying by the Kyodo news agency.
The 24-year old played for Japan at the 2008 Beijing Olympics and made his debut for the national team in a home friendly against Paraguay in September.
Leverkusen are third in the Bundesliga at the start of the four-week winter break, tied on 33 points with Mainz but 10 points behind league leaders Borussia Dortmund.
Japan's Shinji Kagawa (Dortmund), Atsuto Uchida (Schalke 04), Makoto Hasebe (VfL Wolfsburg) and Kisho Yano (Freiburg) alll play in the Bundesliga.