He won’t probably come.
He probably won’t come.
Probably is an adverb of probability. It normally goes in mid position:
- Before the main verb: ‘He probably knows the answer.’
- After the verb be: ‘She is probably at home.’
- After the first auxiliary verb: ‘He will probably call later.’ ‘They have probably forgotten.’
With a contracted negative auxiliary, probably normally comes before it: ‘He probably won’t come.’
Without a contraction, probably goes after the auxiliary and before not: ‘He will probably not come.’