Express disapproval about a doctor providing grass (6)
I believe the answer is:
'grass' is the definition.
'express disapproval about a doctor' is the wordplay.
'express disapproval' becomes 'boo' (I've seen this before).
'about' says to put letters next to each other.
'a doctor' becomes 'bam' (I've seen this in other clues**).
'boo' after 'bam' is 'BAMBOO'.
'providing' is the link.
(Other definitions for bamboo that I've seen before include "Supergrass" , "Tall woody plant" , "Tropical grass with strong hollow stems" , "Mature canes used making furniture" , "Treelike tropical grass" .)