"I am very happy for Marouane because he has had difficult times since he came to the club. But he is a great guy. He trains always the best he can. I am delighted for him," Mata told the British media.
"I think this will be a boost for his confidence. It was good to hear the stadium singing his name because he deserved it."
Fellaini, who lost his place under Jose Mourinho earlier this season, was booed by his own supporters having conceded a late penalty during a 1-1 draw at Everton in December.
"He is a strong man with experience. He is 29 so he has lived so many things in football but it is not nice when you play in your own stadium and you have not the best atmosphere," Mata said.
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"But now it is different and it has changed. I think it is going to be positive for him in the future," the Spaniard added.
Having racked up nine consecutive wins in all competitions, sixth-placed United host rivals Liverpool, who are currently second in the Premier League, on Sunday.
(Reporting by Hardik Vyas in Bengaluru; editing by Amlan Chakraborty)
