Nani's challenge is to be viewed as a force rather than the bit-part player who has to grab opportunity when it knocks. This was the scenario after Phil Jones's misfortune in suffering an ankle injury before half-time allowed the winger to enter at Old Trafford and turn Monday night's FA Cup tie against Reading.

The problem for the principal "could have, should have" performer in the Manchester United ranks is that time ticks on as the clock moves towards six years playing under Sir Alex Ferguson. Consistent inconsistency leads to only one fate under Ferguson: the Scot pointing to the exit, no matter how talented the footballer. Ferguson wants players whose maxim is "control", both of their own fortunes and the team's. Instead, one epitaph that might end up etched on Nani's United CV is "if".

To watch a Nani contribution in the famous red shirt is to turn up to see if it will be a display of the dazzling or frustrating stuff. Monday night's proviso concerned Jones: if not for the injury caused by a clash with Reading's Jobi McAnuff then another long night on the bench beckoned for Nani, the 26-year-old who may possess the largest talent of all of Ferguson's players but who too often flatters to deceive.

During the post-match interview with Ferguson, you could hear the manager still hoping that Nani may yet mature, as his countryman Cristiano Ronaldo did when at United, to tie up a permanent berth in his strongest XI. "He's got great talent, we know that," the Scot said. Like his Lusophone comrade, Anderson, Nani's seasons have been marked by too many sporadic displays.

Nani's first action on joining the action was to up United's game and threaten to break the deadlock. With virtually his opening touch he rocketed a volley past Adam Federici that hit the goalkeeper's right post. Moments later a swivel-and-turn created space for him to sting Federici's fingers with a left-foot dipper that forced a corner.

In the second half, two moments of sorcery in three minutes sealed United's passage to the sixth round to keep the club on the trail of a second treble. First Nani juggled Antonio Valencia's pass with his right boot then smashed home a volley with the left. Then, on 72 minutes, he coasted down the right and pinged over a perfect cross for Javier Hernández to head past Federici.

Anderson said: "Everyone knows Nani's quality. He is one of the good players. We have a good squad with good players. The boss can change it all the time. That is Manchester United." And the issue for Nani: there is always a hungry rival queuing up to prove to Ferguson he should be given the nod instead. The manager added: "I had a feeling he would win the game for us. You could see he was right on form the moment he came on. He had two great strikes immediately and was a threat to them the whole night."

The current campaign has been disrupted by the hamstring problem he suffered playing against Braga in the Champions League in early November, ruling him out until mid-January. "I have been injured for a long time and it is always difficult when you come back, but I've worked very hard and part of what I did on the pitch was because of that," he said following the man-of-the-match display against Reading. "I will continue to work very hard to do my best."

Since signing in the summer of 2007 from Sporting Lisbon for around £17m Nani's record reads: four goals in 41 appearances in 2007–8; eight in 30 (08–09); six in 38 (09–10); 10 in 48 (10–11); 10 in 39 (11–12); and three in 16 this season.

He has won three titles, the Champions League and the League Cup. His tricks and ability to bewitch may also have claimed the hearts of the Old Trafford congregation who love any player touched by genius, but whether their minds are convinced is debatable.

The person who matters, of course, is Ferguson. With Ashley Young, Valencia and Shinji Kagawa all more consistent selections out wide, the manager's January signing of Wilfried Zaha suggests Nani may be playing out his last term at United.

His contract expires at the end of next season. Yet Nani or the club, or both, may decide that he should try and prosper elsewhere. Barcelona or Real Madrid might not be interested but other elite clubs are sure to be convinced they can transform Nani into a man who can finally be a virtuoso on each and every match day.