Digger said to be insignificant (5)
I believe the answer is:
minor
'be insignificant' is the definition.
(similar in meaning)
'digger said' is the wordplay.
'digger' becomes 'miner' (I've seen this in another clue).
'said' indicates a 'sounds like' (homophone) clue.
'miner' sounds like 'MINOR'.
'to' acts as a link.
(Other definitions for minor that I've seen before include "Small-scale - child" , "Little-known" , "Like clubs" , "Of less importance" , "Of small importance" .)