The Australian has looked jaded over the past month or so; his high-energy performances for both club and country coupled with the air miles involved for the latter’s World Cup qualification journey over the past 18 months appears to have finally caught up with him.
Even David Wagner has acknowledged the non-stop football last season and the Confederations Cup last summer for the Socceroos has seen Mooy's form dip and the German boss is at pains to try to alleviate the damage.
But while Town's first Fourth Round clash at home to Birmingham saw the 27-year-old rested there appears to have been no real let up for the player since.
He was back in the thick of it against Liverpool before Wagner was forced to introduce the midfielder on the 30-minute mark against Manchester United last weekend with Philip Billing walking a cautionary tightrope.
Although Mooy looked sharper at Old Trafford and played well on Tuesday night it is still arguably more minutes Wagner would have wanted for such a key player – especially as the mid-week FA Cup clash ran into extra-time.
There is no doubt Mooy is the Terriers’ main creative outlet but with bigger, arguably 'must-win' games on the horizon against the likes of AFC Bournemouth, West Bromwich Albion , Swansea City and Crystal Palace it seemed a massive risk to take at St Andrew's.
Especially as veteran midfielder Dean Whitehead sat warmly on the bench during the bitterly cold West Midlands encounter.
At the twilight of his career, Whitehead may not be able to roll back the years week-in/week-out in the Premier League but surely he could have done a job against a struggling SkyBet Championship side?
At the other end of the age spectrum there are the options of youngsters Lewis O'Brien and Regan Booty – both players who have been promoted to the first-team squad over the course of the past year.
So why not utilise any one of them in the Cup and keep Mooy for the greater good of Premier League survival?
Of course, the issue has been further compounded by the absence of Danny Williams – a dead leg sustained in the first FA Cup clash against Birmingham seeing the combative midfielder ruled out for the past three games.
With warrior Jonathan Hogg likely to be integral to the Terriers relegation fight, perhaps Wagner views him as a slightly more important player to have at his disposal for the forthcoming fixtures.
Whatever the reasoning, it suggests that through a combination of form, fitness and preferences – Huddersfield Town appear a little short in the centre of the pitch.
Thankfully Mooy and Billing (impressive on the night) appeared to come through the Replay unscathed but only time will tell whether it was a gamble worth taking or not....