The Welshman, who moved to the Cardiff City Stadium from Liverpool this summer, has been absent from the Championship club's last two games with a calf tear, which has prompted speculation that the 33-year-old could be close to retirement.
"When we signed Craig we knew we were not going to get 46 league games out of him, that was just never the case," Wales Online quotes Mackay as saying.
"It's not very realistic. I saw nothing in the medical he had before he came here to suggest anything is wrong. I've worked closely and personally with him since he's been here.
"Craig remains a major part of this squad. He has a calf tear now, but is back in training and maybe will be ready for Leeds."