At least the manager knows which one he is now. Only when Rafael da Silva's twin brother Fabio tied the knot and started arriving at Carrington with a wedding ring on his finger, did Sir Alex Ferguson learn to pick his right-back and from his left-back.
The question at Wembley tomorrow is which of the Rafaels will be on show: the right-back who made such a sensational start to last season – operating as a more complete wing-back than most had imagined him to be in his Champions League debut in Denmark against Aalborg, scoring at the Emirates against Arsenal and dominating Robinho in the November 2008 Manchester derby – or the one who has not made the same strides in his second season.
There is little doubt that Rafael is the best right-back at Ferguson's disposal – a more convincing player in that position than John O'Shea and one who now ought to edge out Gary Neville time after time. The club captain's loss of pace can no longer compensate for the occasional accuracy of delivery which offers a reminder of his halcyon days.
But Rafael, who Ferguson signed from Fluminese with his twin in the face of interest from Arsenal's Arsène Wenger, has struggled badly against good opposition – most recently Craig Bellamy in the Carling Cup semi-final second leg and Milan's Ronaldinho last week. His probable contest with Stewart Downing down Villa's left tomorrow promises to be one of the Carling Cup final's most absorbing if – as expected – Ferguson decides to make up for denying the young Brazilian a place in last year's final victory over Tottenham Hotspur by giving him his Wembley chance.
There are signs Rafael does have the pace to operate as a more modern, attacking wing-back than Neville. Paul Parker, United's right back in the 3-1 League Cup final defeat to Aston Villa in 1994, believes that he can get forward and make goals in the way that Glen Johnson has done for Liverpool this season – though Parker views Johnson as comfortably better; the best right-back in England, in fact.
The problem is Rafael's tendency to dive in. He started life as a winger in Fluminese and is yet to get to grips with the defensive side of his game; learning that good defending at full-back is not about winning every challenge but getting close to the player running at you. After probably his most torrid evening yet against Ronaldinho in San Siro, Ferguson admitted this was a work in progress. "He has to learn, against Ronaldinho, that this is the real world," Ferguson said.
But Patrice Evra provides proof that attack-minded defenders sometimes take time to adjust to the defensive side of their game. Evra has described the sensation of feeling like he was in a "washing machine" as he initially struggled with the pace of the English game yet his ability to judge when to go forward and when not to is now a mainstay of his game and Evra has emerged as one of the best full-backs in the world.
Parker's replacement by an emerging Neville in 1995 – despite his own return after 18 months plagued by injuries – demonstrated Ferguson's ruthlessness with the old guard when the young talent he so covets starts materialising and Parker was soon on his way to Derby County. "The manager loves young players who play like old players with bags of confidence," Parker says. "He will always encourage that and make room for them. I remember when I was having my bad patch with injury and it was coming to the end of my time and Gary Neville was coming through. The boss didn't want to set him back by not playing him. He knew my time was up."
Rafael will believe the same goes for his emergence, though Ferguson will have no sentiment for his Brazilian either, if he does not see the development he has come to expect.