The 31-year-old, who has won five titles in Melbourne, crashed out at the quarter-final stage to teenager Sloane Stephens after suffering a back injury in the second set.
The world number three previously injured her ankle during her match against Edina Gallovits-Hall in the first round.
After calling for the trainer during today's match, court-side microphones recorded her telling the doctor it has been "the worst two weeks".
When asked about this in her post-match press conference, Williams explained: "I've had a tough two weeks between the ankle, which is like this big every day, and my back, which started hurting."
She added: "For a Grand Slam, absolutely [it has been the worst two weeks]. Absolutely. Oh, my gosh, I'm almost relieved that it's over because there's only so much I felt I could do. I was unaware the microphones picked that up.
"But, oh my gosh, it's been a little difficult. I've been thrown a lot of balls these two weeks."
Williams has won 15 Grand Slam titles during her career.