Celtic midfielder Shunsuke Nakamura who returned to Japan on Monday and indicated a sore leg may keep him out of a pair of upcoming friendlies against Montenegro and Colombia.
"It hurts when I move my leg and it's pretty tough," Nakamura said after arriving at Narita airport, referring to a sprained right ankle he sustained in the Scottish Cup final against Dunfermline on Saturday.
Celtic defeated Dunfermline 1-0 in Saturday's Scottish Cup final to complete a league and cup double.
Nakamura earned both the Scottish Player of the Year and Scottish Football Writers' Player of the Year awards for his outstanding performance throughout the season.
Japan faces Montenegro in Shizuoka on Friday and then take on Colombia on June 5 in Saitama in its final warm-up for the defense of the Asian Cup in July.
Japan will be bidding for its third consecutive continental crown at the July 7-29 event to be jointly hosted by Thailand, Vietnam, Indonesia and Malaysia.
Ivica Osim's team has been drawn against 2006 Asian Games gold medalists Qatar, the United Arab Emirates and Vietnam.