The 47-year-old actor's former mother-in-law filed a lawsuit against real estate agent Marty Trugman in February, claiming he did not give her a commission on the house that Sheen bought, reported Ace Showbiz.
Trugman is the one listing Sheen as witness. He stated in the document filed in Los Angeles Superior Court last week that Fiore was not the one who introduced the actor to him.
Fiore insisted that she involved Trugman in the sale and was promised a 25 per cent commission. Trugman on the other hand claimed that it was Mueller who introduced him to Sheen.
Mueller will also be a witness in the trial that is set to begin January 7. Both sides have the chance to resolve the matter privately before then.
Back when Fiore filed her lawsuit, Sheen had said that she was "skimming the deal" and if there's money in it then it would go to him or his twin sons with Mueller.
Sheen and Mueller got married in 2008 and their divorce was finalized three years later. Mueller has since gone in and out of rehab for drug and alcohol abuse. She reportedly checked back in rehab earlier this month.