The most common and most likely answer to this crossword clue is the 7 letter word RIVETED
I've seen this crossword clue in The Daily Telegraph
R
I
V
E
T
E
D
Buddy explains!

The straight part
We know that "fascinated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fascinated = riveted.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 RIVETED mean?
RIVETED verb- To attach or fasten parts by using rivets.
- To install rivets.
- To command the attention of.
- To make firm or immovable.