Zac's engage scales with his level. His initial E range is barely large enough to go from red to raptors or blue to wolves. Until roughly level 7 or 8, with Zac maxing his E (which is also his only source of damage), basic wards around your lane should be fine to protect you.
If you can't manage that, use your CC ability to remove his only form of initiation and mobility for up to 24 seconds at a time (until lv 9, when his E is on a 12 second cool-down, and reaches roughly from the edge of dragon into Red buff camp (for relative distance, that's raptors to middle of mid lane, or barely large enough to get into a lane without using the tribush on whichever side blue buff is on).
If all else fails, you get a handy dandy indicator as soon as he appears on your screen as to where he's going to land. Walk out of it, which should be easy if you have boots, any sort of speed boost, or mobility.
Zac's abilities all cost a not-inconsiderable amount of health, of which he can be deprived by stepping on his blobs. Once his E is gone pre-6, you have no reason to fear him. Once his E is gone post-6, you have his ultimate to worry about, which applies a 1 second knockback ONCE, and otherwise a 20% slow.
Zac is perfectly manageable and in a fine spot right now.