Brought down by rebuilding, I'd allow (4,3)
I believe the answer is:
laid low
'brought down' is the definition.
(I've seen this before)
'rebuilding i'd allow' is the wordplay.
'rebuilding' indicates an anagram.
'id'+'allow'='idallow'
'idallow' anagrammed gives 'LAID LOW'.
'by' is the link.
(Other definitions for laid low that I've seen before include "Stricken" , "Put out of action by illness" , "Hid away" , "Brought down" , "Indisposed" .)