Borussia Dortmund midfielder Shinji Kagawa has said he would "fight more" if he were to relive his time at Manchester United.
Kagawa, 27, signed for United from Dortmund in 2012 but he struggled for form at the club, scoring six goals in 38 Premier League appearances.
The Japan international returned to Dortmund in 2014 and has since impressed for the Bundesliga club with 14 goals in 57 league games.
Asked by FourFourTwo how he would reflect on his time at United, Kagawa said: "I was still young, just 24 or 25. I had a lot of experiences there and that helped me grow, and looking back I wasn't concerned about anything, just focusing on doing the best I could.
"Of course there were good players there but everyone thinks differently; the Dortmund coach is the Dortmund coach, and the Manchester United coach is the Manchester United coach, and I just have to accept how everything went."
Asked what he would do differently, he replied: "Fight more, every day -- even a small player like me should fight every day to succeed at a club like Manchester United and it's the same now at Dortmund.
"I just have to focus on how I can get better every day to try to succeed at this level. Of course, you also have to be mentally strong."
Kagawa added that he is "not thinking" about a return to the Premier League amid reports of interest from Liverpool, where former Dortmund boss Jurgen Klopp is currently in charge.