In his book Ric Flair: To Be the Man the former WWE star said he suffered from alcohol-related heart issues, and early reports suggested his heart is the reason he's in hospital now.
Rory Karpf worked on filming ESPN's 30 for 30 documentary on Flair, which is set to premier in November, and he also tweeted to ask people to keep the 68-year-old in their prayers.
Flair is a legend of the wrestling world and one of the most recognisable figures on the planet.
He is widely considered the best professional wrestler of all-time, having been a 16-time world champion.
"The Nature Boy" was a fixture of the National Wrestling Alliance (NWA) and won a total of 31 different championships across his in-ring career.
Flair wrestled for World Championship Wrestling throughout the mid to late 1990s boom period of wrestling, where he led the promotion against the World Wrestling Federation, now WWE.
The legend did make a switch to WWF in 1992, before returning to WCW a short time later.
When WCW was purchased by the WWE in 2001, Flair eventually made his way back to the Vince McMahon led operation.
His last official match in the WWE was in 2008, losing to Shawn Michaels at WrestleMania XXIV. He was officially inducted into the WWE Hall of Fame the same year.
Most recently Flair has returned as a manager for his daughter, Charlotte, who is a four-time RAW Women's champion.
He remains contracted to the company on a "WWE legends" deal that allows the organisation to use him in its programming, as well as produce merchandise in his likeness.
Only last week, Flair was used to promote the USPGA Championship, appearing in the opener of US netwoek TNT broadcast.
