Venus Williams' career is in a downward spiral that she seemingly can't reverse, again raising questions of her retirement.

Several media outlets reported Thursday night that Venus and Serena Williams pulled out of doubles competition just before their opening match at the Australian Open, citing a left leg injury to Venus.

The withdrawal comes three days after Venus' opening-round singles meltdown against No. 22-ranked Ekatarina Makarova in three sets in Melbourne.

ESPN.com reported that Serena said after the withdrawal, "I would love playing doubles, I love playing with Venus. Sometimes it doesn't work out but I'm sure we'll be back next year."

The validity of that statement is subject to debate.

Bleacher Report stated that the elder Williams sister has not advanced past the fourth round of a major tournament since 2010. A year later, she revealed that she was diagnosed with Sjogren's syndrome, an autoimmune disorder that results in fatigue and muscle pain.

No reason was given for the Venus' injury. No reports indicated that Venus was injured during or after her first-round loss to Makarova. She pulled out of the Hobart International tournament in early January, less than 24 hours after she lost in the ASB Classic final in Auckland.

The Hobart tournament director told ESPN he did not believe Venus sustained an injury in Auckland and was just going to rest instead for the Australian Open.

Williams currently is ranked 37th in the world and was as low as 105th in 2011.

"The last 12 months I have had [health] issues," ESPN reported her as saying after her early exit from the Australian Open, "but this year I definitely am looking forward to having a good run and feeling well.

"Health is a factor for any professional athlete, so I don't think I'm any different from anyone else," she said.

The feeling apparently lasted three days.

After the withdrawal was announced, Bleacher Report surmised, "However, at age 33, you have to wonder how much the seven-time Grand Slam singles champion has left in the tank."

Williams has been asked why she continues to play despite her diagnosis and the fact that her game is not nearly what it once was when she was the top-ranked player in the world.

"I love tennis. It's fun," she said, according to ESPN. "I think pretty much anyone who plays tennis will say that they enjoy the game, so I think that is definitely motivation for me, something that I enjoy."