Neil Harris cast uncertainty over Neil Etheridge's Cardiff future by dropping him for the derby draw with Swansea before suggesting one of his goalkeepers will be leaving the club in January.
Etheridge has played over 100 games for Cardiff since joining the club in 2017.
But the Philippines international – who has been linked with West Ham as potential cover for the injured Lukasz Fabianski – was omitted for Sunday's 0-0 draw with Swansea as Alex Smithies took over in goal.
"I won't go into too much detail at the moment," Cardiff manager Harris said. "There's been a lot of talk around Neil, not just in this window but in the previous window as well.
"I had a really good couple of conversations with Neil in the week about his standards and what he wants to get back to. I think it's been a little bit up and down.
"We've got three goalkeepers who all deserve to play first-team football and three don't go into one, so something will have to give before February 1."
Cardiff have Etheridge, Smithies and former Newport goalkeeper Joe Day on their books.
Swansea, who had their former striker Oli McBurnie, now at Sheffield United, watching on in the away end, were chasing the first league double in the 108-year history of the fixture.
The Swans won the reverse fixture at the Liberty Stadium in October and went close to snatching the lead when Bersant Celina struck a post in the first half.
Cardiff substitute Callum Paterson headed against the crossbar in the second period, but the game petered out to a disappointing goalless draw.
"I have to be honest, after losing the first game we certainly didn't want to lose back-to-back derbies," said Harris, who refused to discuss interest in Kieffer Moore after Wigan manager Paul Cook revealed on Saturday that Cardiff had made a £2.3million bid for the Wales striker.
"I knew we'd be at it from the first whistle because we had to respond from the QPR game (when Cardiff lost 6-1 at New Year's Day)."
"In the first half we played some decent stuff on quite a tough pitch," Cooper said. "The grass was long, but that's fine, that's their prerogative."
Asked if the grass may have been kept longer to hinder Swansea's passing style, Cooper replied: "That's not a question for me to answer. Christmas period maybe, people days off, I'm not sure."
Cooper was more forthcoming about the performance of Liverpool loanee Rhian Brewster.
The England Under-17 World Cup winner made his debut after signing in midweek for the rest of the season.
"It was a difficult game for him, but we saw glimpses of his athleticism, his mentality and his willingness to be positive," Cooper said.
"It was a good experience for him, but he is here to deliver too and I felt he did a good job for the team."