Celtic boss Tony Mowbray has challenged his centre-halves to prove they deserve to be in his team following the 2-1 defeat by Rangers.
Mowbray has been alternating his defensive pairing this season, with Glenn Loovens and Stephen McManus given the nod at Ibrox ahead of Gary Caldwell.
However, poor defending contributed to both of Kenny Miller's goals and Mowbray wants to see an improvement in the coming weeks.
"The central defenders at our club have to stake a claim and show me they possess quality week-in, week-out to take this club where we want it to be," said Mowbray.
"But that is all over the pitch, everyone has to step up to the mark because if we want to win the SPL more often and be a power in Europe, we have to develop and if the individuals can't step up to the mark then we will change them.
"Centre-halves like to find the guy they can play alongside for 40-odd games or however many games you play in a season.
"It's not the case at this moment because there are no two who are doing particularly brilliant.
"They must stake their claims, so that one of them is going to sit on the bench all season alongside me because the other two are keeping clean sheets and doing their job."
Mowbray continued: "I said after the Rapid (Vienna) game that I had concerns - what do you want me to do?
"The team is ready, the team is prepared and we go out and concede early goals.
"If they had made the goals, with good inter-change and movement then you hold your hands up but that was never the case so the concern is there.
"I haven't seen the goals, after I have looked at them again I will make up my mind as to who was at fault, who allowed balls to bounce and who was in the wrong position.
"Football is about putting demands on your players and they either rise to the challenge of the demands you put on them or they don't.
"Each of them have had opportunities and will continue to have opportunities.
"The day they keep clean sheets, and look solid and do well, the same two will play the next week."
In a typically fiesty Old Firm encounter, Shaun Maloney and Mark Wilson were both booked for diving inside the Rangers box after respective challenges from David Weir and Sasa Papac, but Mowbray scoffed at referee Craig Thomson's decisions.
"I will sit and watch it back," Mowbray said. "If the referee thinks they are dives then so be it.
"But Mark Wilson diving to win a penalty? It makes me laugh.
"Mark Wilson is the most honest guy you have ever met, the most gentleman-like person you will ever meet.
"It doesn't matter. I would never question the officials' integrity, they do their job to the best of their ability and we accept it and get on with it."