The most common and most likely answer to this crossword clue is the 9 letter word NEEDFULLY
I've seen this crossword clue in The Daily Telegraph
N
E
E
D
F
U
L
L
Y
More clues leading to the result NEEDFULLY
- Fuelled stove in city as required
- Of necessity, fuelled convertible in US city
- Engineer fuelled in US city as a requirement
- Essentially, muddled Nelly engaged in silly feud
- Born on the day one goes for full replacement necessarily
- Necessarily Spooner asks you to give the fool some food
- Necessarily led fuel riot in New York
Buddy explains!

The straight part
We know that "as a requirement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as a requirement = needfully.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.