The Blades are in search of a new manager following the dismissal of Danny Wilson in April and since the seasons end have been linked with a number of managers who are currently in and out of work.
McCall, a former player with United under the reign of Neil Warnock had dismissed any speculation linking him with the Bramall Lane hot-seat but following an approach to the Fir Park club it is understood that the SPL club have granted permission for United to speak to their manager.
McCall said: "It's a story that's not worth speaking about because it's all speculation. "I've never as a player, coach or manager sought to go elsewhere. I've always been happy here and if anything at all ever comes up and is put to me that is the time we'll talk about it, but at this moment in time it's been pure speculation.
"I think when you've had a decent season, or a couple of decent seasons which I've been fortunate to have, then speculation will grow. As far as I'm concerned, my full focus is on here all the time."