As Juan Mata stood on the touchline waiting to come on late in United's defeat at Vicarage Road, there was widespread bemusement when Antonio Valencia's number flashed up as the one to be replaced.
Wayne Rooney had ambled through another game where he not only failed to contribute in any way but actually hindered the efforts of his United team-mates.
The team as a whole were poor but there are no words that can be suitably used on this blog to describe how bad Rooney played.
His decline was illustrated more vividly than ever before when Luke Shaw sprayed the ball wide for his captain- perhaps a little overhit but by no means out of Rooney's reach.
Rooney sluggishly wandered to the ball but a woeful first touch sent it straight out of play.
Soon after, he overhit a simple five yard pass to the onrushing Marcus Ashford and then gave possession straight back to Watford after United had tried to launch a counter-attack.
It was nothing new and in fact epitomised the 30 year old's performances so far this season.
Bar fleeting moments of brilliance against Bournemouth and Hull City, which have rescued him from a public mauling, if you take away that goal against Bournemouth and assist at Hull, his performances this term have been as poor as we saw on Sunday.
Whether it has been in midfield or up front, Rooney's propensity to slow down his side's attacks have been a major problem.
Predicting it all before all of us, perhaps, was Sir Alex Ferguson, who allowed the player to move on at the end of the 2012/13 season only for Moyes- in a desperate attempt to pacify his ill-fated tenure, oversaw the signing of new five year contract for the player.
It persisted under Louis van Gaal with the Dutchman also retaining him as club captain.
There was nothing wrong with that decision, but the bewildering declaration that Rooney would play- no matter what- absolving him of any past, present and future misgivings on the pitch, was a worrying trend.
Perhaps when United were labouring under Moyes and van Gaal with a squad largely bereft of attacking ingenuity, it was overlooked.
Now, with Paul Pogba and Zlatan Ibrahimovic suffering from his rotten form, it is finally being thrown into the spotlight.
Rooney lacks the poise to sit deep in midfield, his short passing range is not good enough and too often it leaves United overrun in the middle of the park.
Hopeful balls to pick out Antonio Valencia down the right are not enough.
This certainly isn't a sudden, sharp drop from England's most capped player of all time but it certainly does appear to be one that has woken everyone up to how destabilising Rooney's presence can be.