The most common and most likely answer to this crossword clue is the 8 letter word KNEADING
I've seen this crossword clue in The Daily Telegraph
K
N
E
A
D
I
N
G
Buddy explains!

The straight part
We know that "action of a masseur" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case action of a masseur = kneading.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KNEADING mean?
KNEADING verb- To work and press into a mass, usually with the hands; especially, to work, as by repeated pressure with the knuckles, into a well mixed mass, the materials of bread, cake, etc.
- To treat or form as if by kneading; to beat.
- (of cats) To make an alternating pressing motion with the two front paws.
- To mix thoroughly; form into a homogeneous compound.
- The process by which something is kneaded.