Following Larsen's opening, it's me in check (5)
I believe the answer is:
limit
'check' is the definition.
(limit can mean to check or restrain)
'following larsen's opening it's me in' is the wordplay.
'following' means one lot of letters go next to another.
'opening' suggests taking the first letters.
'me' becomes 'mi' (both are spellings of the musical note).
'in' is an insertion indicator.
The initial letter of 'larsen' is 'l'.
'it' going around 'mi' is 'imit'.
'l' next to 'imit' is 'LIMIT'.
(Other definitions for limit that I've seen before include "maximum number" , "Restrict - boundary" , "Keep in" , "Cap" , "Place bound on" .)