Has fitness guru Richard Simmons completely fallen off the grid? According to TMZ, the 66-year-old hasn't been seen in public for an entire year and his friends are extremely worried. Sources told the site that Simmons has been battling depression because of a serious knee injury.

TMZ reports that Simmons hasn't been photographed in public since a charity event on Jan. 11 and he abruptly stopped communicating with friends. Reportedly, he even has his housekeeper turning away people who come to visit.

Sources also claim that Simmons hasn't been showing up to his Beverly Hills fitness studio and no one knows why he's been MIA.

"A source extremely close to Richard - one of the few people with whom he is in contact - tells TMZ the fitness guru is in a massive state of depression over a bum knee. He says doctors told Richard he needs a left knee replacement and if he doesn't get one he will never be able to exercise again," the site wrote.

The source claims Simmons is terrified of surgery and has put it off for an entire year. Reportedly, he tried to fix his knee problem but undergoing stem cell and red blood platelet therapy but it didn't work.

"We're told he's paralyzed with fear and depression, which has made him a shut in for 2014," TMZ claims.

Other people close to Simmons believe the issue is not just an injured knee but fear there could be bigger problems. If Simmons is battling depression and hiding out, he's definitely not hinting at it on social media.

He's been very active on Twitter over the last few months and even posted a picture of himself with Gwen Stefani.

"Feeling Hella Good with the gorgeous Gwen Stefani," he captioned the photo.

Simmons' last tweet was on Nov. 12 in which he wrote, "Age proof your muscles by doing cardio workouts 3 days a week and strength training 3 days. (Use that 7th day for a good hour long walk)." 

Update: Simmons released a statement via his publicist thanking fans for their continued support.

"I am so touched by the outpouring of love and concern I have received today. I had had a tough time dealing with this injury, as it is keeping me from doing what I truly love to do and that is teach classes around the world. I know I will see you all soon!"