Afraid there's the devil to pay out! (7)
I believe the answer is:
panicky
'afraid' is the definition.
(similar in meaning)
'the devil to pay out' is the wordplay.
'the devil' becomes 'nick' (Nick and Old Nick are names for the Devil).
'out' indicates putting letters inside.
'nick' inserted within 'pay' is 'PANICKY'.
'there's' acts as a link.
(Other definitions for panicky that I've seen before include "(Irrationally) fearful" , "nervous!" , "Inclined to lose head" , "Very worried" , "in a tizzy" .)