Huddersfield have had something of a fairytale since German boss Wagner joined the club in November 2015, winning promotion from the SkyBet Championship last term with one of the smallest budgets.
Clark managed Town between 2008 and 2012 and admits it'll be a huge success if his former side can maintain their top-flight status.
"The biggest problem for [Huddersfield] will be that David Wagner is a man very much in demand,” Lee Clark said.
“Dean Hoyle, who's a top guy and a magnificent owner, has been fighting off bigger clubs for 18 months and it's only going to get harder.
"If Huddersfield stay up, it will be an incredible achievement and he will be one of the managers of the season.”
The game this weekend will be of a twist of emotions for Clark who was born in Newcastle and spent the majority of his playing career at the club, over two different periods.
Clark also went on to speak about the contrasting expectations of both clubs this seaon.
On the two side's aspirations, Clark said: “Fourth bottom isn't what [Rafa Benitez] would have wanted back in August, while staying up is a cause for celebration in Huddersfield's case.
“Knowing their owner and his ambitions he'll see that as the start of a journey."
And whatever the outcome tomorrow afternoon, the former midfielder believes both sides have what it takes to beat the drop.
"Newcastle will survive this year and I'm backing Huddersfield to do so as well but then the two clubs have another battle on their hands holding on to their managers - and that's one I want them to win too."