United's summer signing pulled out of Japan's 1-0 win over Iraq last night an hour before kick-off after feeling a twinge in his lower back in training the previous day.
The winger said: "I underwent treatment for as long as possible before the match and (Japan coach Alberto Zaccheroni) waited for me.
"I felt a twinge and didn't want to take the risk.
"It's not a serious injury and I don't think it will keep me out for long.
"I can walk without any problem but if I put strain on it it still hurts."