dead man walking

Short definition from Wiktionary

Noun

1. 1
   A condemned prisoner walking to a death chamber or other place of execution.
2. 2
   Someone who is soon to die.
3. 3
   Someone who is about to face an unavoidable loss (though the person may not realize it).
4. 4
   A multivortex tornado typically appearing in the form of a human figure walking.