Younes Kaboul has unquestionably been one of the shining lights so far under Sam Allardyce's tenure after the French defender's error-prone, rusty start to his Sunderland career.
But the loss of a solitary player through illness shouldn't have such a seismic effect. Oh-how-dearly Sunderland need another central defender in the January transfer window.
For all Sunderland made a fist of it after Sam Allardyce had switched to a 4-5-1 set-up after just 19 minutes and could easily have come away with something if they had benefited from a slice of fortune, they ultimately paid the price for a return to slapstick defending in the opening exchanges.
Billy Jones is no central defender. It was no coincidence the only goal of the game came down that side.
Without Kaboul's presence in the back three, Watford looked a threat every time they ventured forwards early on - doubling up on Sunderland's wing-backs and delivering three excellent crosses, one of which they scored from.
At least, Allardyce reacted to the circumstances and sacrificed DeAndre Yedlin to bring on Jack Rodwell in the middle of the park, with the ex-Manchester City man enjoying one of his better afternoons.
But the damage had been done by that start.
On another day, Sunderland would have levelled proceedings, yet for the second Saturday running, they were made to rue a lack of precision with their finishing.
Fabio Borini and Adam Johnson should both have done much, much better with golden chances.
The only Sunderland player who looked like he had the conviction to find the net was Jermain Defoe, with the England international denied by a quite brilliant reverse save from Heurelho Gomes.
Perhaps Defoe was not fit enough to start after shaking off his hamstring injury. Perhaps he only had 20 minutes in his legs.
Yet what a difference the 33-year-old made. The Watford defence were immediately wary after his introduction.
The primary idea behind switching to three at the back was to accommodate Defoe in a front two and surely there has to be a return to that at Chelsea next weekend.
But Sunderland head to Stamford Bridge on the back of a defeat which will kid no-one about how damaging it was to the Black Cats' survival bid.
With Chelsea, Manchester City and Liverpool next on the horizon, this was an almighty set-back for Allardyce.