The 28-year-old has not started a league game for the Toffees since the opening-weekend draw with Watford and reports this week hinted he could look elsewhere for more regular football in order to boost his quest to make Belgium's Euro 2016 squad.
Mirallas moved to Merseyside in 2012 and in the summer he signed a new contract to keep him at the club until 2018 having scored 11 times last year.
Martinez insists the forward remains an integral part of his plans and predicts he will have a big impact for Everton in the coming months.
"It couldn't be further from the truth," Martinez said of the notion Mirallas was unhappy.
"Kevin has been a very, very important player while I've been at the football club
The start of this season has been challenging for him because he had a couple of niggles then he had the sending-off so wasn't available for three games
But the way that he's been working in training has been very impressive
"He's improved as a footballer and it's important for us that Kevin is fresher now going into the second half of the season and we'll get the benefit from that
"Kevin Mirallas is a very, very important player for Everton - he knows that
What he needs now is to get playing time because the start of the season has been frustrating for him."
Martinez also stressed that keeping Mirallas and his team-mates together will be his main mission when January comes around.
The form of this weekend's opponents West Ham, along with Leicester and Southampton, has made the race for Europe even more competitive but Martinez will avoid the temptation to make any major changes in the transfer window.
"We've got such a strong squad - the focus for us is to see how good we can be with the squad we have now," he added.
"We have enough time in the summer to see if we can bring players into the football club
All we want is to be as good as we can with the players we have, that I'm delighted with.
"It will be very important for us to make sure the window that is going to open in the winter is to just give a bit more normality, to make sure the squad gets reaffirmed, looking at the younger groups more than the first-team level to make sure that we get a clear 10-month competition out of this squad.
"It will be the summer when we reassess where we are and where we should go
I wouldn't look at the winter as a moment to make significant changes."
Martinez confirmed Bryan Oviedo's bad luck with injury has continued, with a hamstring strain now set to keep him out for two to three weeks, but Leighton Baines is unlikely to slot in at left-back against the Hammers.
The England defender is back in full training following his ankle injury and will feature in a behind-closed-doors friendly over the international break.
Source : PA