Everton have struggled defensively so far this term.
Centre-halves Michael Keane and Yerry Mina made a decent start in the first few games, but the partnership has begun to look shaky in recent weeks.
Despite their height, they are not dominating as many hoped they would.
They have been particularly disappointing in terms of defending set pieces, conceding five times already.
Both will need to step up their games going forwards, or Marco Silva will bring the partnership to an end with Mason Holgate waiting in the wings.
Everton do not have much cover after they failed to re-sign Kurt Zouma on a permanent deal, so perhaps they ought to look at some options in January.
One man who could be worth pursuing, is Galatasaray defender Christian Luyindama.
Luyidama is reportedly a target for both West Ham United and Wolverhampton Wanderers (Fanatik), after impressing for the Turkish club.
Luyindama spent last term on loan from Standard Liege before making his move permanent this summer, and he looks to be a good, physical defender.
The ace – who has featured in the Champions League – would cost in the region of 15 million/£13 million to sign, making him a cost-effective acquisition that could come in and lay down a challenge to the starting centre-backs.