The pair had been subject to reports earlier this week that they enjoyed an on-set romance while Jennifer was married to Brad Pitt.
US magazine Star quoted Matt’s dad, Paul, as saying: "He even had a relationship with one of of the girls...Jen.
"They would make out in the dressing rooms. He told me about it - it was when she was married to Brad Pitt."
However, Jennifer has now vehemently denied the allegations.
Her spokesperson told MailOnline: "I have commented in the National Enquirer and others. It's 100 percent false.
"Jennifer has never had a romantic or sexual relationship with Matt LeBlanc."
Jennifer was married to Brad from 2000 to 2005, when he ended their marriage to begin a relationship with Angelina Jolie, who he later married in 2014.
Jennifer and Matt’s ‘Friends’ characters, Rachel and Joey, enjoyed a brief fling on-screen in the ninth and tenth series of the US sitcom, which ended in 2004.
Jennifer is now engaged to Justin Theroux, while Matt is currently single after splitting from girlfriend Andrea Anders in January, having been married to model Melissa McKnight from 2003 to 2006.