Unknown champ goes topless for nothing (4)

I believe the answer is:

zero

I'm a little stuck... Click here to teach me more about this clue!

'nothing' is the definition.
(I know that nothing can be written as zero)

'unknown champ goes topless for' is the wordplay.
'unknown champ' becomes 'ze' (I can't justify this - if you can you should give a lot more credence to this answer).
'goes topless' means to remove the first letter (I've seen 'go topless' mean this).
'for' becomes 'pro' (as in being 'pro' or in favour of something).
'pro' with its initial letter taken off is 'ro'.
'ze'+'ro'='ZERO'

Can you help me to learn more?

(Other definitions for zero that I've seen before include "Nonentity" , "A very low temperature" , "Very bad visibility" , "Rock bottom" , "Loser" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.