Reports suggested the Republic of Ireland international, who is having his best season at Goodison Park and is the club's second-highest scorer with seven goals, was in advanced talks to be reunited with former boss David Moyes at Old Trafford.
However, Martinez dismissed the speculation and said they were looking to reward the younger players who had progressed under his leadership.
"It must be a different Seamus Coleman because we've not had a conversation with anyone," said the Spaniard.
"Seamus has been having a very good season and we want that to continue and in the next 10 games it is important he carries on with the same levels he has shown, developing his football.
"He is becoming a very important player at Everton and he will become a very important player for his national team and we want Seamus to be here for a very long time."
Martinez has stressed previously that contract talks with a number of players will not be concluded until the end of the season because he wants the squad to focus on matters on the pitch.
Scaremongering in the media would not change that stance he said.
"We always work very consistently behind the scenes, everything goes accordingly to the effort and performances of the players, and it is not down to media speculation," the manager added.
"The players we have at the club now we have a clear strategy of how we want to keep this club together.
"We have a new generation coming through, we want to keep the senior players for as long as we can.
"It will not change for any media speculation. We will always reward young players who do well and as they change their role within the squad it is only normal to be rewarded."
Everton announced on Thursday they had extended their shirt sponsorship with Thai beer company Chang, although their £16million-plus club-record deal over three years is dwarfed by the likes of Arsenal and neighbours Liverpool, at £30million and £20million a year respectively.
Martinez said he did not expect that to change his summer transfer plans, with their league finish likely to have more effect on policy.
"Whatever happens in the summer will be the next step but many of the decisions will depend on how we do in the next 10 games so you can imagine the focus goes into those games," he said.
"To be able to sign a new three-year deal is exciting for both parties but it doesn't change anything (on transfers).
"It is not a real worry or concern; whatever the finances will be we will be strong enough and good enough to make us better every window."
However, negotiations on new signings are likely to be complicated as there is a World Cup to contend with.
"You have different areas in the market. There are a group of players you want to sign before they go to the World Cup, others you want to wait and see if they have a bad World Cup so you can get them for a cheaper price," said the Spaniard.
"It depends on what type of player you are looking for but the World Cup always affects one way or another the valuation of a player."
Martinez would not be drawn on whether he was looking to bring in players who would be involved in Brazil.
"You always want to bring in good experience but the way the modern game is going you need the fresh legs and naivety of young players and we have a good balance at present," he said.
"We don't want to lose any of the top performers in this group and I do feel this group needs to stay together to fulfil their potential.
"We will see what gaps open up in the summer."