Could be dearth of fibre (6)
I believe the answer is:
thread
'fibre' is the definition.
(I've seen this before)
'could be dearth' is the wordplay.
'could be' is an anagram indicator.
'dearth' is an anagram of 'THREAD'.
'of' is the link.
(Other definitions for thread that I've seen before include "Strand, cord" , "clothes casually cut" , "Line of cotton - plot (of book, film)" , "Cord - Internet chat room discussion" , "Twine" .)