Roberto Martínez will consider offers for Nikica Jelavic and John Heitinga in January while wishing to strengthen Everton's forward and midfield options when the transfer window reopens.

The Croatian striker and the Dutch defender, who also operated in central midfield under David Moyes, have barely featured this season and their places at next summer's World Cup are in jeopardy as a result. West Ham United and Crystal Palace are both interested in signing Jelavic on loan with a view to a permanent transfer – though Everton are not keen on a temporary deal at present – while Heitinga, one of the club's highest earners, has not played one minute of Premier League football this term.

Martínez's priorities for January are to replace the long-term injury casualties Darron Gibson and Arouna Koné, although not Gerard Deulofeu, who is out for approximately two months with a hamstring tear. And he admits Jelavic and Heitinga could leave providing it is not to the detriment of the Everton squad.

The Everton manager said: "We have had conversations because it is important to know how the players feel but in the same way they are fighting to get into the team they understand that, if they don't play minutes, it will affect their World Cup chances. Because they are such good professionals I have to consider that and need to see that. But it's a balancing act that we don't weaken the squad.

"That's what we are going to do in January. I am quite open-minded about it. If the right thing appears for the players I will have to consider it and look into it. Always bearing in mind that we can replace them and make the squad in a strong position."

Everton had said Deulofeu would be missing "for a few weeks" following his injury against Fulham but that has been revised to "six to eight weeks" by Martínez after the 19-year-old underwent tests at his parent club, Barcelona. But Martínez said: "What I would like to do in January is replace Darron Gibson and Arouna Koné, like-for-like in terms of positions and for the short term rather than long term because those players will be big players for us in the future. It's not about Gerard; I'm not concerned with his short-term injury. We have players in the squad ready to come in."

Under the terms of Deulofeu's season-long loan the fee Everton pay to Barcelona reduces the more games he plays. But his injury lay-off will not hit Everton's finances. Martínez explained: "That is when the player is fully fit. The deal is about the player being fully fit and available for selection. When he is injured it doesn't count, so it's fine on that.

"You don't want to lose a player but I feel Gerard will have a massive impact in the final third of the season. If he had been playing the whole season, he might have struggled for the last two months because he has never been in a demanding league. You want that sort of player fresh for that period so I am quite happy with the way it's worked out really."