Worry, seeing it in a portal (7)
I believe the answer is:
agitate
'worry' is the definition.
(thesaurus)
'it in a portal' is the wordplay.
'in' means one lot of letters goes inside another.
'portal' becomes 'gate' (I've seen this before).
'a'+'gate'='agate'
'it' placed within 'agate' is 'AGITATE'.
'seeing' is the link.
(Other definitions for agitate that I've seen before include "Disturb or shake" , "Keep moving" , "Stir violently" , "Perturb" , "'Stir, excite (7)'" .)