The world number three was forced to retire in the second game of her singles match against France's Tatiana Golovin and though she returned to win the mixed doubles with compatriot Novak Djokovic, her movement was very restricted.
"I stretched to hit a backhand I think and went back to push off to the next side and that's where I felt really sharp pain," Jankovic told reporters after Serbia's 2-1 win over France.
"It was like somebody put a knife in my glute.
"It's a strain. It was really, really painful. I thought I had torn a muscle or something. I have to be ready for Melbourne, which is most important and I don't want to risk any kind of injury."
The Australian Open begins on Jan. 14 and Jankovic admitted that when she suffered the injury she had feared the worst.
"I was really concerned and right away I went to the hospital and got all these tests and I'm really glad that I don't have a torn muscle.
"When I got taped for the doubles, in the beginning I was doing okay but as the match went on longer, I started to have pain in my back. Then it got lower and went all over the place."
LACKING FITNESS
Jankovic, who had acupuncture treatment after the mixed doubles, said her lack of preparation after a nose operation at the end of last year meant she had arrived in Perth below full fitness.
"I am not really ready," she said. "I only had two weeks before I came here so obviously my body is not in the best shape and the best form.
"I need to do a lot of work to get to where I want to be, to where is my limit and where is my potential. Right now I'm not really feeling that great. I am not really that fit. It's unfortunate that I got this muscle strain today."
"I think I recover quite fast and that's something that's good for me. I will try to do my best to be in good shape. I am really hungry to play matches. I want to be in the best form for the Australian Open."
Jankovic will make a decision on Thursday over her further participation in the Hopman Cup
