Shinji Kagawa admitted Sunday he thought long and hard before leaving Manchester United to rejoin Borussia Dortmund.

"It was a very difficult decision for me," Kagawa said, after signing a four-year deal to June 2018 with the eight-time Bundesliga champions a day before the transfer deadline.

"Dortmund's style of football really suits me. I made the decision because I felt strongly about wanting to help this team achieve things again."