A newcomer in 'Pilgrim's Progress' (5)

I believe the answer is:

sprog

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'a newcomer' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'in pilgrim's progress' is the wordplay.
'in' indicates the answer is hidden within the clue.
'SPROG' can be found hidden inside 'pilgrims progress'.

Can you help me to learn more?

(Other definitions for sprog that I've seen before include "Infant" , "Baby (slang)" , "Child; recruit (mil. slang)" , "Kid" , "little one" .)

I've seen this clue in the Evening Standard.

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