Down to two options
marco or zoro
outside of zoro fights number 2 etc theres really no set up for zoro vs king
like there was with queen and sanji
which led to the obvious
now for zoro like i said there isnt actually any set up for king
but could obviously still happen
now to marco
king and marco have a few parallels
both introduced in a pair
they both were asked by another yonko to join yet refused
they both knocked big moms ship off the waterfall
all that without the obvious aesthetic similarities
fire flying related fruits the "yc1" etc
now for sanji oda repeated the same thing he did in enneies lobby (with the same chapter difference!)
From a Reddit comment:
"Chapter 403, Sanji was defeated by Kalifa, Nami replaced the fight and complimented him. 10 chapters later, chapter 413, Sanji made an appearance and saved Usopp from Jabra. Then he made a speech to boost Usopp's confidence.
Chapter 1005, Sanji was captured by Black Maria, Robin replaced the fight and complimented him. 10 chapters later, chapter 1015, Sanji made an appearance and saved Chopper from Queen. Then he made a speech to boost Chopper's confidence.
now as i pointed out when i responded to that post in the main thread
the role of zoro in ennies lobby is actually being held by marco
He held off King and Queen (kaku and jabra)
And kept chopper (ussop) safe long enough for sanji to come in and save chopper (ussop)
as i said the set up is for a 1 vs 1 with marco and king
so the only way i see king vs zoro is if he beats marco