Webster and Zaliukas are out of contract at the end of the season, and there have been suggestions the centre-halves could be sold to raise funds in the New Year.
Hearts boss McGlynn concedes players may have to be sacrificed in order to help the club out financially, but is determined to hang on to the 'backbone' of his team.
"It's massive for us to keep them," said McGlynn. "They are the experience in the team and they're both international centre-backs.
"You will never actually know how much you appreciate them until they aren't there. They do a tremendous job and it would be a blow to lose them.
"I'm not suggesting we will but at the same time if offers come in for players and everyone is happy with them, then it may well be that some players go.
"I can't say who that will be. The board of directors would firstly need to accept an offer and then the player in question would have to agree to go.
"It's very much ifs and buts at the moment on that issue. But I've got to say that Andy and Marius are the backbone of the team right now and no manager would want to lose that."
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