I don't feel Miquel is even an option. Defensively, he just isn't tough enough.
An ideal fit into the fourth choice role would be a young player with lots of potential who'd get games in patches when others are inevitably injured and try and compete with and eventually replace Mertesacker or Vermaelen.
Djourou was an ideal fit until we/he realized that he probably isn't going to replace the first choices.
We've suffered enough when we had the likes of Sylvestre and Squillaci as fourth choices. To present that position to Miquel would be downright stupid as the fourth choice WILL have to step in for a spell at some point in the season.