Enthusiastically get knee surgery to play regularly (6)
I believe the answer is:
keenly
'enthusiastically' is the definition.
(I've seen this before)
'knee surgery to play regularly' is the wordplay.
'knee surgery' becomes 'keen' (I can't explain this - if you can you should give a lot more credence to this answer).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'play' are 'ly'.
'keen'+'ly'='KEENLY'
'get' is the link.
Can you help me to learn more?
(Other definitions for keenly that I've seen before include "Eagerly, sharply" , "With eagerness" , "In an eager manner" , "Eagerly, enthusiastically" , "With enthusiasm" .)