Singer in corner worried about nothing (7)
I believe the answer is:
crooner
'singer' is the definition.
(I've seen this before)
'corner worried about nothing' is the wordplay.
'worried' indicates an anagram.
'about' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'corner' anagrammed gives 'croner'.
'croner' enclosing 'o' is 'CROONER'.
'in' is the link.
(Other definitions for crooner that I've seen before include "Singer like Bing and Frank" , "Singer of sentimental songs" , "Profession of Bing, Frank or Perry" , "Singer of quiet songs" , "Sentimental balladeer" .)