Brewer's Dictionary of Phrase and Fable/Sick Man
Sick Man (The). So Nicholas of Russia (in 1844) called the Ottoman Empire, which had been declining ever since 1586.
"I repeat to you that the sick man is dying; and we must never allow such an event to take us by surprise."—Annual Register, 1853.
N.B. Don John, Governor-General of the Netherlands, writing in 1579 to Philip II. of Spain, calls the Prince of Orange "the sick man," because he was in the way, and he wanted him "finished."
"'Money' (he says in his letter) 'is the gruel with which we must cure this sick man [for spies and assassins are expensive drugs]'."—Motley: Dutch Republic, bk. v. 2.