The third seed and former winner stumbled and fell during the first set against Edina Gallovits-Hall but recovered to thrash the Romanian 6-0 6-0.
She admitted she was uncertain of the state of the injury which was almost identical to the one which forced her withdrawal from last year's Brisbane International.
"I think I was really, really close to panicking because a very similar thing happened to me last year, almost on the same side, the same shot," Williams said.
"So I almost panicked, and I thought, I can't do that.
"I just have to really remain calm and think things through."
Despite taking an injury timeout while ahead 4-0 in the first set, Williams returned to complete the emphatic win, but her movement was kept to a minimum.
She may have scans to see if there is any structural damage but is hoping for the best.
"That's definitely optional. I'm going to play it by ear," she said. "I would love to see the next few hours how I go, and then I'm going to decide what to do next at that stage."
"Obviously there's pain, obviously there's swelling. So it's going to be really important to see how the next few hours unfold."
"You know, I have a day. I have a day to work on it."
The 31-year-old said she would have to work mentally as well as undergo physical rehabilitation over the next 24 hours.
"I feel like with my experience, I feel like I've gone through a lot, and that I just have to mentally adapt," she said.
I've been able to mentally adapt to a lot of things.
"It will be a good challenge and almost a good game for me to mentally adapt to this.
In some ways, she said she would rather not know the extent of the problem.
"I know one year I won this tournament and had two bone bruises in both knees," she said. "I had no idea. I just knew I was in pain.
"I think sometimes what you don't know cannot hurt you."
Defending champion Victoria Azarenka beat Romanian Monica Niculescu 6-1 6-4 after a shaky second set.
"I started well but I struggled a little in the second set," Azarenka said. "But I'm glad I'm still winning."
Earlier Danish star Caroline Wozniacki overcame a wildly erratic Sabine Lisicki to squeeze into the second round.
The former world No.1 and 10th seed, was baffled by Lisicki's high-risk game before finally winning 2-6 6-3 6-3.
Lisicki managed to hit 33 more winners than the Dane - but was hobbled by her unforced errors - 57 compared to eight.
Meanwhile, Japanese veteran Kimiko Date-Krumm rolled back the years to pull of a major upset.
The 42-year-old crushed 12th seeded Russian Nadia Petrova 6-2 6-0 in just over an hour, to become the oldest woman in professional tennis to win a singles match at the Australian Open.
Italian seventh seed Sara Errani's Open campaign also ended quickly as she was sent home after a 6-4 6-4 loss to Spain's Carla Suarez Navarro.
Russia's Maria Kirilenko, seeded 14th, managed to keep the draw on an even keel when she defeated American Vania King in straight sets while eighth seed Petra Kvitova beat Italian Francesca Schiavone 6-4 6-2.