Zoro would need at least high/extreme-diff to beat King.
1) King doesn't even need to show his hybrid form/mask completely undamaged to beat Marco.
For YC1 tier, Ben > Shiryu (with invisible DF) > King > Marco > Katakuri
2) Zoro is probably 80-90% recovered due to zou medicine, but def not 100% healthy. So he already has a bit of a handicap vs. king.
3) I expect Zoro to be very badly damaged after King's fight. King will inflict sizable damage onto Zoro. On top of that, his medicine will diminish in effect rapidly. Zoro will be barely standing by the end of the fight.