The Belgium international arrived at Old Trafford as David Moyes' first marquee signing in September 2013, but the former Everton midfielder struggled to find his form as injuries hampered his progress.
When fit, Fellaini was far from the midfield powerhouse who had impressed at Goodison Park and the 26-year-old came in for criticism at his lack of consistency.
Fellaini failed to find the back of the net in his 21 appearances for United and admits it could have gone better, but is determined to show his worth under new manager Louis van Gaal.
"Everybody knows my club season was one to forget," he said. "I'm the same Marouane.
"United signed me one year ago. There have been some positives and some negatives, like the bad injury I picked up. Also, our team didn't quite click into place.
"But now we have a new manager, we'll see what happens next season. In the meantime, I am concentrating on my national team.
"I don't play here (the FIFA World Cup) for a transfer. We'll see with the new coach, but I still feel good at United."
Fellaini showed his quality in Belgium's opening FIFA World Cup game on Tuesday as he came off the bench to begin the side's fightback against Algeria, with Marc Wilmots' men eventually winning 2-1.
