The Belgium international has endured a difficult first campaign at the Red Devils following a £27.5m move from Everton on transfer deadline day last summer.
I need to be fit to be good. Even when I am injured I can play but the fitness is not the same
Fellaini has made one assist in 16 Premier League appearances this season, prompting criticism from former United stars and disgruntled Red Devils supporters.
But the 26-year-old pointed to a three-month injury lay-off as a key factor in his poor performances.
“I will look to show what I can do next season. When this season finishes I will start with my preparation for the next year and it will be good,” Fellaini told the Telegraph.
“I need to be fit to be good. Even when I am injured I can play but the fitness is not the same. I was injured for three months and that was a difficult moment for me.
“When you arrive in a new team you want to play, you want to stay with the team and when you can’t play it is difficult to see the team – even off the pitch.”
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