Former Queen guitarist finally producing strain (5)
I believe the answer is:
exert
'strain' is the definition.
(thesaurus)
'former queen guitarist finally' is the wordplay.
'former' becomes 'ex'.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'finally' indicates one should take the final letters.
The final letter of 'guitarist' is 't'.
'ex'+'er'+'t'='EXERT'
'producing' is the link.
(Other definitions for exert that I've seen before include "Make a great effort" , "Cause (oneself) to make a strenuous effort" , "Work strenuously" , "Bring into play, wield" , "Bring into use, strength or influence" .)