Most likely.

I have to shut Josh in a room alone for 1-3 days if I even so much as bathe another cat, let alone if one has to go to the vets. If I don't he'll even attack his own sisters then the whole house gets in an uproar.

If Ozzy is being calm (since he just had surgery) I'd let him stay out and shut Molly in a room by herself for a day or two. If Ozzy is being a pill then reverse it.

During the separate time, try brushing each one then taking that brush and use it on the other one without cleaning the fur out first. Kinda helps them reaquaint themselves with their smells. Some people just rub a cloth over each one and do it that way.

Good luck.

**edited to add** When you do attempt to let them be together again, make sure to supervise them to make sure they won't start fighting again.