LONDNO: Midway through the second half here, just as the fourth official stepped forward clutching his board ready to announce a Manchester United substitution, Wayne Rooney was released into space down the Vicarage Road touchline. As he trundled forward, Marcus Rashford and Zlatan Ibrahimovic accelerated into the Watford box, anticipating a fizzed ball across the face of the goal or a cunning pull-back to feet. Neither came. Instead Rooney ballooned his attempted cross high into the stand behind the goal.
In itself, that was all the evidence required to suggest that the number to be illuminated on the substitution board had to be 10. Jose Mourinho has never been a manager who is afraid of removing players who have just made critical errors. And Rooney's wastefulness was a critical error.
After a listless first hour, United had finally counter-attacked their hosts with something approaching the fluency and zest for which they were once renowned. Here was a real opportunity to conjure up an equaliser to Etienne Capoue's fierce opening goal. Instead, Rooney undermined the revival with the kind of leaden-footed delivery that would draw the coach's criticism, even in an under-10s game.
However, the bad news was that that one incident was by no means the low point of the United captain's contribution. Almost wholly peripheral to the action, Rooney was about as mobile and effective here as an oak wardrobe. Yet, when the number came up to signal who Juan Mata was to replace, it was not 10 it was 25. To the bemusement of everyone gathered in the stadium, Antonio Valencia was removed from the fray, not the man who had long been by-passed by the action.
My, Rooney was poor here. He did not even have the excuse of being tired after Thursday evening's Europa League defeat by Feyenoord; this was a game for which he had been specifically rested. Never mind a midweek trip to Rotterdam, Rooney played like he had just returned from a long weekend in Amsterdam.
Surely, after this Mourinho has to acknowledge that his faith in Rooney has has run its course. Slow of thought and legs, United are a side currently functioning as if running through custard. And much of the blame lies with the continued selection in the most critical position in the team of a man who is playing on his reputation.
In the attempt to counter Watford's physical presence, Mourinho had picked a team of giants. But size, clearly, is not enough. And with Maroaune Fellaini, Ibrahimovic and, above all, Rooney playing together centrally, all the pace in the side was pushed out to the wings.
Yet that left Unable unable to seize the initiative in the middle, and at times Capoue had so much time and space in midfield that the Watford playmaker was in danger of succumbing to agoraphobia.
Rooney's singular failure to be where it matters, to provide drive, to put some fuel in the team's engine, was central to United's stuttering inertia. The only time you were even aware that he was on the field was when he arrived, inevitably moments after the action had subsided, to complain vociferously about a decision by referee Michael Oliver.
To compare Rooney's performance with that of David Silva in the same position for Manchester City, is to understand why United are so far behind their neighbours. From Silva flows much of City's creativity; with the imagination of his supply, the Spaniard makes his colleagues play better. He may be no quicker over five yards, but Silva is constantly involved in the game in vital places, an ability which long ago appears to have deserted Rooney.
After losing his third game on the trot, Mourinho attempted to be philosophical. He suggested that the three wins his team accrued at the start of the season were misleading. He said he knew his is a side that needs work.
It would help if he could field another 10 Marcus Rashfords. The teenager's neat, clever interchange with Ibrahimovic that preceded his goal - precisely the kind of sharp thinking that now seems beyond his skipper - suggested a real way forward for Mourinho: play the two together down the middle, and leave Rooney out.
True, Rooney is not the only problem Mourinho faces. He must surely have come to realise that playing Fellaini and Paul Pogba together is not working: they are about as compatible a partnership as Nigel Farage and Jeremy Corbyn.
But the most pressing issue is at the creative heart of this United side. It has to be sorted and sorted quickly. Sir Alex Ferguson knew it more than three years ago. Yet, still it appears to be beyond his latest successor to grasp: the hard truth is that Wayne Rooney is no longer worth a place in the Manchester United team.