Cuellar's current deal runs out this summer but McLeish wants the former Rangers player to extend his stay. The 30-year-old has been used effectively at right-back and left-back recently in addition to his preferred centre-back role.
McLeish confirmed: "I think there have been talks (about a new contract) and they will be ongoing. I've said to Carlos it's important he keeps playing as well as he can and then contracts won't be a problem for him. If he produces the form he is capable of, we will get more clean sheets so why would you want to let someone like that go."
McLeish has again hinted he would not rule out a return to Villa for striker Robbie Keane whose loan spell from Los Angeles Galaxy ends after this weekend's game at Wigan.
Keane has scored three goals in five starts and impressed in a deeper role behind Darren Bent.
McLeish said: "Will Robbie return? I don't know. We have to see where we are in terms of recruitment in the summer but Robbie has had a good influence on the place.
"Where he is right now probably has a glamorous feeling about it but at the same time he's got a bit of adulation from Villa fans so maybe that has probably whetted his appetite."