Australia are waiting to learn the extent of a knee injury suffered by Cadeyrn Neville, while they will have to do without Darcy Swain (suspension), Izack Rodda (foot), Jed Holloway (calf) and Ned Hanigan (knee).
McKellar says they must show their strength in depth.
"I think what makes it seamless is the preparation we've done over the past three-four weeks and understanding whoever's playing will be involved heavily in preparation over that period of time," he added.
"You can't be throwing your eggs in one basket thinking they'll get through a series. The game is played at an incredibly high intensity these days, very physical, and sadly we've seen a fair few injuries.
"We've been unlucky in that area and every now and again you get clusters in a position, you just have to make sure your whole squad is prepared and ready to step up if required."
