Manchester United midfielder Shinji Kagawa admits he wishes he could have contributed more to his side's Premier League title winning season.
Kagawa, who arrived at Old Trafford from Borussia Dortmund last summer, started his debut season at United brightly but suffered a knee injury in October which kept him sidelined for two months.
The 24-year-old scored five goals in 18 Premier League outings for the club, including his hat-trick in the 4-0 success over Norwich last month.
The Japan international has earned plaudits in his home country after helping United to a 20th league title but believes he could have offered more to Sir Alex Ferguson's side.
He said: "I was looking to produce even more results. I was injured and I felt things didn't go well easily.
"I had a lot of conflict, frustration and worries. In that sense, I think it has been a profound year.
"Honestly, I haven't contributed as much as I did at Dortmund.
"I was even injured. I still don't quite have that feeling of accomplishment."
Despite feeling he could have offered more on an individual level, Kagawa was pleased to be part of three successive title wins after helping Dortmund to back-to-back championships following his move from J-League club Cerezo Osaka in 2010.
The midfielder is hoping to build on that tally, adding: "I've managed to win three in a row. I think my career is bound to get better and better."
The Reds boast victories against Sheffield United, Coventry and Preston in their debut season in League One, without conceding a goal, and Barker believes that speaks volumes for the progress they have made.
"It's fantastic that we've beaten clubs like that. The challenge for us now is to do it on a regular basis," he said after an early strike from Mike Jones clinched victory at Broadfield Stadium on Tuesday night.
"We've got an opportunity now to reach 70 points and finishing as high as seventh. We've won three of our last four games and want to make it four out of five in our final game at home to Hartlepool on Saturday."