I will shortly be sick (3)
I believe the answer is:
ill
This clue is a double definition.
'i will shortly' is the first definition.
(abbreviation; 'shortly' indicates an abbreviation)
'sick' is the second definition.
(I know that sick can be written as ill)
'be' is the link.
(Other definitions for ill that I've seen before include "Unwell from bacillus" , "I will (abbrev.) (1'2)" , "Wicked" , "poor" , "Evil or sick" .)