Mirallas has had an injury-plagued first season in England.
"He's had a lot of niggles. He's nearly not quite adapted to what the Premier League means and how the games go," Moyes said.
"I look at him and he's signaling to me with 15 minutes to go - so maybe he's not quite got what's required at Everton or the Premier League.
"What he has got in abundance though is pace, ability, he can score goals, he can take you on and he can play in two or three different positions."