Mirallas has scored in three of Everton's last four Premier League games as they bid to secure a place in European competition for next season.
However, the 25-year-old striker, who missed three months of the season with a hamstring problem, is continuing to suffer from injury niggles and seems unable to play for a full 90 minutes.
"I look at him and he's signalling to me with 15 minutes to go - so maybe he's not quite got what's required at Everton or the Premier League," Moyes told the Liverpool Echo.
"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.
"But we're finding that we're getting 60 or 70 minutes into games and thinking will he keep going? Will he pick up an injury? Will he lose concentration?
"His ability is not in question but there are a lot of players who can take time to get used to the Premier League."
Moyes believes Mirallas needs to learn this aspect of the game from certain members of his team.
He said: "When you stay at Everton for a time it gets you used to it. Look at how Marouane Fellaini has recently played with injuries, look at Phil Jagielka and Tim Howard.
"That mentality grows on you when you have been here a while, so when you're new to it maybe he's not aware that's what you do at Everton. We need people to play in two or three positions which he can do - but quite often you have to go out there when you're not always at 100 per cent."
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