The singer has claimed she didn't know about having to potentially perform again in the results show.
There was a Strictly controversy in Week One when Anastacia was ruled unable to dance due to injury.
As a result, Melvin Odoom was sent home.
Speaking this week, Anastacia made the surprise confession: "In Dancing With The Stars in America we don’t have a dance-off and Len [Goodman] and Bruno [Tonioli] are there, but I didn’t know [there was a dance off on Strictly]”
Anastacia insisted she would have done the dance off if she could have but said her injury was one 'not to be messed with'.
“If I could have done the dance-off. We know how to get through a show. This is not the typical injury you want to mess with,” she told ITV's This Morning.
Meanwhile, chatting on It Takes Two earlier this week, Anastacia admitted she was shocked to avoid the latest bottom two last Sunday.
She told Zoe Ball on the BBC Two spin-off show: "I totally thought we were going in [to the Dance Off again]. I was like, 'OK, what moves do we have to clean up?'
"Because we're like the bottom feeders, I thought that was just who we were."
Her pro partner Brendan Cole agreed: "We were like, 'Yeah, it's us. Get on with it'. But what a great feeling!"
Anastacia continued: "I was super grateful that people voted for us, so I was even more happy.
"I was like, 'oh my God, there's a few people out there that like us!'"
Strictly Come Dancing is back this Saturday night on BBC One from 6:30PM.