Small volume about one pursuing girl is a masterpiece (7)
I believe the answer is:
Here is my best explanation:
'a masterpiece' is the definition.
(I have seen 'Literary masterpiece ' mean 'classic' so perhaps 'masterpiece' could also mean 'classic')
'small volume about one pursuing girl' is the wordplay.
'small volume' becomes 'cc' (cubic centimetre).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'pursuing' means one lot of letters go next to another.
'girl' becomes 'lass' (lass is a kind of girl**).
'i' put after 'lass' is 'lassi'.
'cc' placed around 'lassi' is 'CLASSIC'.
'is' is the link.
(Other definitions for classic that I've seen before include "Quintessential", "Timeless-quality work; a race", "Having qualities like those of acknowledged art", "Serving as a standard - of the highest quality", "Work of enduring excellance", "Flat race", "Time-honoured", "Derby, say", "Simple, neat and elegant" and "Good example of its kind".)