Tish and husband Billy Ray filed for divorce earlier this week and speculation soon began that she had started sleeping with Michaels after he and Miley recorded a racy duet together last year.
However, Michaels's spokesperson insisted that the rumours are purely "fabrication".
"Several reports of my client having an affair with Tish are unfounded and a fabrication. He has been a close friend of the family for some time because of his work with Miley," the rep explained to E! Online.
"It's unfortunate that Billy Ray and Tish have to be further tainted by these lies being reported. The only relationship he's had with Tish is professional because he worked with Miley on 'Every Rose'. She recut it, and obviously they did that together at [Good Morning America] in the summer, and his song 'Nothing To Lose' on his current album."
Tish's camp have also spoken out against the rumours, saying in a statement: "It's not true. They had a working relationship."