According to sources, there's been tension between the pair ever since Week 1's dance off controversy.
Anastacia and Brendan were in the bottom two in the first results show where she was ruled unable to dance due to injury. As a result, Melvin Odoom was sent home.
The Sun newspaper now suggest that Anastacia's ongoing injury has prompted rows in the training room.
"Brendan is not the most patient of dancers," an insider claimed. “They’ve had to tweak all their dance moves because of her injuries – they can’t even do any lifts or sudden turns.
“His previous partners like Natasha Kaplinsky, Lulu, and Kirsty Gallacher have dealt with his outbursts, but Anastacia doesn’t take any crap and fights back."
The source added: “But both are determined to make their relationship work on the dance floor and move up that table.”
It's seemingly quite a change from the couple's first few days on the show.
Speaking last month, Anastacia and Brendan appeared to be getting along like a house on fire.
"Every single partner on the show is very different," Brendan said on It Takes Two. "I love this girl, we're excited, we talk a lot in training, we need to do more dancing..."
"I think we're like a bromance!" exclaimed Anastacia.
Brendan added: "She just loves being on here, there's no agenda here apart from being a dancer!"
Strictly Come Dancing 2016 continues this Saturday night at 6:30PM on BBC One.