The Queens Park Rangers defender has been linked with a move to the Stadium of Light.
The problem, however, is that it's hard to justify the thinking behind such a bid...
Certainly, the lack of options is a factor. Sunderland, if they are indeed interested in the QPR centre-back, have clearly identified the 24-year-old as a man short of game time who could be very available.
But, just because someone is available, it doesn't mean they'll make a good signing. Fans at the Stadium of Light need some inspiration from somewhere, not just a move that *might* work out if they hope for the best.
You could say it's an admirable approach from Sunderland to continually look at out-of-favour players and do just that. But, while they are in the relegation zone, it's a naive one.
Younes Kaboul may have put in some good performances but what about Sebastian Coates? The Black Cats have enough passengers in their defence and form suggests Caulker would simply be another one.
QPR fans en masse seem to have had enough of him, while Southampton supporters have been left widely disappointed in Caulker since his loan move, too. Even those who want him to stay justify that with the fact he is cover - not because he is showing any kind of form.
Form and fitness are perhaps the biggest barriers to success if Sunderland want the QPR man. Even if the 24-year-old was good in his prime, he is nowhere near his best right now. It was easy to see why Southampton shouldn't have loaned Caulker. It's even easier to see why the Black Cats shouldn't buy him outright.