Manchester United midfielder Shinji Kagawa admits he is concerned that his lack of regular playing time at Old Trafford is affecting his form for Japan.
Kagawa has struggled for first team action this season but was still able to help Japan secure their place at the World Cup next year.
The former Borussia Dortmund player has featured in just one Premier League game for the Red Devils so far this season - the 2-1 defeat against West Brom at Old Trafford last month, where he was withdrawn at half-time.
Kagawa featured for Japan in their recent friendlies against Serbia and Belarus, and admits that not playing regularly for Manchester United could impact on his performances for his country.
“There's a matter of fitness and there's also that atmosphere of playing for my country,” he said.
"It's different from the atmosphere at Manchester United, but you still get a good feel for being on the pitch when you play regularly.
"Maybe it's because I'm not used to being on the pitch of late, but I didn't feel like I was able to enter these two games properly.
“During tough times like these I have to improve myself.
"Personally, I felt strongly after these two matches (against Serbia and Belarus) that I need to play more and, as a team, there are many things we need to do.
"We all need to go back to our European or J-League clubs and take what we learned in these two matches and work to fix those problems.”
Manchester United resume their Premier League campaign against Southampton at Old Trafford at the weekend. David Moyes's side currently sit in 9th place in the Premier League after seven games.
Moyes, who took over from Sir Alex Ferguson in the summer, has previously insisted that Kagawa is part of his first team plans.