Play aggressive early and deny him stacks. He has one of the worst early games ever, so you can take advantage of that by playing an early game champ to snowball or an aggressive ganking jungler to kill him and snowball.
Nasus is only strong when you let him get strong, from my experience and from watching lots of evidence from videos, Nasus is absolutely useless if the enemy laner snowballs the lane and denies Nasus a shit ton of stacks.
Either don’t go alone when Nasus is not visible on the map or play a champ with multiple dashes or kiting options to help keep the fed nasus far away from you.
His lifesteal is very small in the laning phase btw, pots and biscuits are his main form of regen when he is getting poked a lot or the enemy is trading a lot. If you have trouble with his regen rush a grevious wounds item or go ignite and use it on him when he uses R.