The risk about Carroll is his injury proneness. History proves that tall strikers tends to have more injuries. If Carroll is also an injury-prone player (his record wasn't very good here already), he'll never fulfill his potential that worhts 35m. In addition to that, once the injury brings permanent obstacles to his aerial powerness, he's finished.
In fact, if I am the manager, I would rather make his training schedule become lighter rather than heavier.