Suaalii is the headline acquisition at the Waratahs following last year's wooden-spoon campaign, but his heroics on Australia's Spring Tour have given hope he can spark a revival under former Brumbies coach McKellar.
Signed for a deal worth close to $1.6million per year, the 21-year-old Suaalii has so far lived up to the billing in rugby union with impressive performances for the Wallabies.
The former Sydney Roosters star was named man of the match on debut at outside centre as Australia recorded their first win over England at Twickenham in more than a decade.
But McKellar - returning after a stint coaching English club side Leicester - says the Waratahs can't look to Suaalii to be their knight in shining armour.
"It's madness to think that an individual - we're not playing under 8s here - is going to do it all on his own," McKellar said on Thursday.
"He needs others. He needs his forward pack to provide a good set piece and a platform for him.
"If he does that, then he can play off the front foot off whoever's inside him.
"He's going to rely on others.
"It (the gameplan) is not just going to be; 'get the ball to Joseph and let's go back to the halfway line', because that's not going to work."
There remains a question mark as to where Suaalii will line up come the Waratahs' opening Super Rugby fixture against the Highlanders on February 14, with the British and Irish Lions tour now just a matter of months away.
Suaalii said on Thursday he was comfortable anywhere across the backline and expressed an eagerness to deputise for Tane Edmed as a goalkicking option.
McKellar won't be taking orders from Wallabies coach Joe Schmidt over where best to deploy the cross-code convert and wants to keep the Waratahs' gameplan for Suaalii under lock and key.
"I've got some ideas (where Suaalii will play) but I'll keep it as a surprise for now," McKellar said.
McKellar isn't expecting to hear from Wallabies coach Joe Schmidt (l) on where to play Suaalii (r). (Mick Tsikas/AAP PHOTOS)
"It'll be no different to how it's been in the past. I'm not going to tell Joe (Schmidt) what to do, and he won't tell me what to do.
"If we're talking about individuals, we'll do what's best for individuals.
"It's always been that way, and you've got to work together, and come back to what's best for the player.
"There'll be no issues there, butting heads with Joe wanting us to coach a certain style or that sort of thing."
Among those the Waratahs will look to provide Suaalii the platform to wreck damage out wide will be Taniela Tupou.
The Waratahs are confident new-signing Taniela Tupou (c) will hit the ground running in round one. (Elias Rodriguez/AAP PHOTOS)
The tighthead prop has joined the Waratahs after the Melbourne Rebels folded.
"He's a point of difference player, isn't he? That's the job ahead of us and 'Nela' over the next few weeks he can hit round one in a good headspace and shape," McKellar said.
"He's a big, happy, lovable character so when you see that side of him you know good things are ahead."
