Kerber said that others aspects of her game were not affected, but felt pain as she arched her back to deliver her serve.
The 25-year-old revealed that she has been struggling with the problem for a few days, adding that treatment from the trainer did not help.
"It was my back, and I will go after here to the physios and to the doctor, and then I will see what's going on there," BBC Sport quote Kerber as saying.
"I could move; that was fine. But just my serve, when I go back, there is a lot of pain there. I actually feel it like two, three days.
"So I was thinking it will be maybe not too bad, but in the first set I was feeling that and it was actually worse and worse. Also I take the treatment but it was not too good."