The 68-year-old actor plays gay pianist Liberace in the film, while Matt plays his lover Scott Thorson, and Michael was impressed with how well the younger actor handled their hot tub scenes.
Michael told the Hollywood Reporter: "We did have a lot of pages in the hot tub. But Steven is very tasteful, and we have had a couple of sections choreographed so as not to embarrass anyone. We just got it on.
Look, I so tip my hat to Matt. I know in my prime, I don't know if I could have done what he does here."
Michael chose to appear in the film as it had an emotional depth and resonance, rather than just being a camp romp.
He added: "We knew, with [director] Steven [Soderbergh], this was not going to be about winking at the audience. It was not going to be La Cage aux Folles. This was a relationship between two people who loved each other a lot.
"I swear after a few minutes of watching it, I forget it's Matt and myself, and then I literally forget it's two guys.
"In their arguments in Richard La Gravenese's screenplay, you can hear a married couple having at it."