Worried Russia's ready to invade Thailand's borders (8)
I believe the answer is:
troubled
'worried' is the definition.
(similar in meaning)
'russia's ready to invade thailand's borders' is the wordplay.
'russia's ready' becomes 'rouble' (Russian currency - 'ready' can mean money).
'to invade' means one lot of letters goes inside another.
'borders' says to hollow out the word (remove centre letters) (only the edge or border letters remain).
'thailand' with its centre removed is 'td'.
'rouble' placed within 'td' is 'TROUBLED'.
(Other definitions for troubled that I've seen before include "Anxious" , "Disquieted, upset" , "Disturbed, bothered" , "Distressed, perturbed" , "Inconvenienced" .)