Netherlands international defender Heitinga has made just two Capital One Cup appearances so far this term, while Croatia striker Jelavic has featured seven times in the Premier League, without scoring.
Everton boss Roberto Martinez knows the pair are eager to press their World Cup claims ahead of the Brazil finals next summer.
If he could find the right replacements, he would not stand in the way of the duo's exit, but he insists the fifth-placed Toffees must keep the 'right balance' in their squad to maintain their push at the top of the table.
He told the Liverpool Echo: "It's fair to say that, as a football club, we understand Niki and Johnny's positions.
"They've been such great professionals for us that we need to make sure we look at it from their point of view.
"It's a World Cup year and we need to understand that. From the club's point of view too, though, we need to make sure we get the right balance.
"If they are here (after January), I'll be delighted because they bring more than just when they play.
"They have a massive influence on what we do on a daily basis even when they're not playing.
"But if there is an opportunity which works for them, then we need to look into it.
"We can't weaken the squad though. That's the balancing act. But we have to be open-minded - they deserve that."
Martinez insists the club is under no pressure to sell prized assets such as Leighton Baines in the upcoming January transfer window, and he remains relaxed about the situation.
The former Wigan boss said: "When you are in a football club and you are in a position where you have to sell to balance the books then, yes, you don't want anyone to call you or anyone to make any offers.
"But we are in a different position. We don't have to sell any players and anything that will be done will be to benefit the squad and to get us into a stronger position. In that respect, I'm very relaxed.
"I want teams to take notice of our players because that is a very good sign that we are doing things well, but that will never put me in a position of difficulty.
"It is the opposite, it is what I want - to see the players developing, playing good football and attracting compliments."