As Rafa just posted, there is a reason that clubs have been cautious about him. He may have played quite a lot, but there is more of a risk that he'll have a short career than others. Hence he is more of a risk than others, so we shouldn't be spending too much on him, or banking on him.
I think it is naturally a worry. But 13 mil and Ba in exchange for Carroll is still a deal well worth making for me.