Whether this had been hindering Erakovic enough for her to make the 15 unforced errors in the first set compared to her opponents six is uncertain, although Erakovic did hit one more winner than Halep - seven to six.
Listen: Erakovic on her first round exit
The New Zealander was broken in the first game of the second set and then really appeared to struggle with her movement and it didn't get much better as her Romanian opponent reeled off the next two games before Erakovic was forced to call it quits and withdraw from the match after 47 minutes of play.
"The last few days it's been doing really well and feeling good. The legs been doing well and I've been hitting the ball well. It's probably the big occasion against someone like Halep you need a lot more of yourself," the world number 99 said.
"I just think it sprung on me in the middle of the set and it just got worse and worse and I just move well enough and compete. It's very, very disappointing."
"The injury is mainly to do with putting a load on my right knee and trying to spring from the knee. I was a the stage of thinking it was behind me and just a niggle. I just didn't think it was this bad to make me retire."
Erakovic is still scheduled to play doubles with Brit, Heather Watson later in the week.
