Mirallas was on the mark again in the draw at Tottenham last week.
"The guys did a fantastic job against Spurs and Kevin was fantastic against Stoke and Tottenham," Fellaini told the Liverpool Echo.
"It's his first year in the Premier League so he's still adjusting to the tackles and the intensity of it. It's not the same as in Greece.
"It takes time to get used to it but next year he will be even better. I don't need to speak to him - he knows."