To me, if he Play Sergio Ramos and Canavaro at the sametime, then should be find. But come to certain "Set Piece" especially the Corner Kick, the Physical Strength for the above two players may in disadvantage.
Therefore, i believe he has know this Weak Point by Brought-in Christian Metzelder (German International) with the Height of 19+cm. But if you put Metzelder to play with Sergio, Then Sergio may have to compromised on the attacking option.
That's simply Metzelder would not be suitable to play as a Single Defender's (Last-man before Keeper). The German International do not have the Speed!!But i saw his Positioning and Arieal Ball Control are very good.
Another Option, if you put Metzelder to Play with Canavaro, that may be the Best way especially when Real are facing a Strong Attacking Team like Barca and Arsenal. Both Canavaro and Metzelder are very very good in Tackling and Man-marking.
Therefore, at the same time the Fans may not be Happy simply due to the fact that Sergio Ramos are Real Madrid "Future Hope" and the Fans may want to see him in the Field as far as he's not Injured.
Again, if you are the Coach in one day, this are the Problem where YOU nned to Resolve and Facing day by day!!!! Thank You........