Bodybuilder in port, perhaps - a German one (7)
I believe the answer is:
protein
'body-builder' is the definition.
(I've seen this before)
'port perhaps a german one' is the wordplay.
'perhaps' is an anagram indicator.
'a german one' becomes 'ein' (I've seen this in another clue).
'port' is an anagram of 'prot'.
'prot'+'ein'='PROTEIN'
'in' is the link.
(Other definitions for protein that I've seen before include "Organic compound, essential constituent of living cells" , "Substance in meat" , "Essential part of diet, found in meat, say" , "Combination of amino acids in living things" , "A body chemical; pointer (anag.)" .)