Very likely to be disembowelled? That's fatal! (6)
I believe the answer is:
deadly
'that's fatal' is the definition.
(similar in meaning)
'very likely to be disembowelled?' is the wordplay.
'very' becomes 'dead' (dead can mean very or absolutely, eg 'dead wrong').
'to be disembowelled?' means to remove the middle letters (I've seen 'disembowelled' mean this).
'likely' with its centre taken out is 'ly'.
'dead'+'ly'='DEADLY'
(Other definitions for deadly that I've seen before include "Lethal or mortal" , "Lethal, capable of killing" , "There are seven such sins" , "sniper aspires to be" , "Lethal, capable of causing fatal injury" .)