World number five Angelique Kerber has revealed that her back injury severely impacted her ability to serve against Ekaterina Makarova.

The German failed to make it past the fourth round of the Australian Open for the second year running, losing 5-7 4-6 to the 19th seed.

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."

Makarova will now play the winner between Kirsten Flipkens and Maria Sharapova.