In the saddle, master travels against the current (8)
I believe the answer is:
upstream
'against the current' is the definition.
(synonyms)
'in the saddle master travels' is the wordplay.
'in the saddle' becomes 'up' (as in up on a horse).
'travels' indicates anagramming the letters.
'master' with letters rearranged gives 'stream'.
'up'+'stream'='UPSTREAM'
(Other definitions for upstream that I've seen before include "Eats rump (anag)" , "contraflow" , "Current trend is not" , "at an earlier stage in process" , "Facing current" .)