Though it will strike some as heresy, there is a case for suggesting that Cristiano Ronaldo goes to the Champions League final in Moscow with quite a lot to prove. No objective witness could think of questioning the unanimity of acclaim that has recognised Manchester United’s Portuguese phenomenon as far and away the main man of the English football season, as easily both the most entertaining and the most productive player in the Premier League. That he is rightly festooned for the second year in succession with just about every worthwhile personal award available to him in this country is a natural, if unnecessary, reminder of how fortunate we are to have such a dazzling amalgam of skills, surging athleticism and competitive enthusiasm at work among us.

Yet, for all who have most fervently expressed admiration, anything less than a highly influential contribution from Ronaldo at the Luzhniki stadium will undoubtedly be a blow to the testimonials. If he is disappointing, we will be obliged to go on admitting that he has yet to develop the habit of representing the immensity of his talent adequately on the biggest of football occasions. His ability to do so was demonstrated in the 2006 World Cup semi-final between France and Portugal in Munich, where he played superbly throughout the hour and a half as his nation went down to a Zinedine Zidane penalty. But how often has he reached and maintained that standard when involved in the most dramatic, high-stakes confrontations with top-quality opposition for his club? Not often enough would be a legitimate assessment, whether we are considering the Champions League or the few collisions of true heavyweights that occur in the domestic arena.

Many will say it is unjust to look for evidence of greatness beyond that provided by the wonders he has already wrought on behalf of United this season: the extraordinarily sustained run of match-shaping performances and 31 goals that have been decisive in keeping the Premier League championship trophy at Old Trafford; the seven European goals that have done so much to set up Wednesday’s showdown with Chelsea in a distant capital. It’s true that even if we allow for how plentiful cannon fodder is in our flagship league – and note that of the 66 goals he has amassed there over five seasons only one was inflicted on Liverpool and none on Chelsea – his ever-rising strike rate was never less than impressive and has soared breathtakingly in the past two years, with a scoring total of 17 in 2006-7 and now the stunning 31. For a wide player, somebody who has to be a maker as much as a taker of goals, that last figure is close to miraculous.

His haul from the current Champions League campaign is also formidable, especially as it is almost double the four he had previously accumulated for United in Europe. So is it fair to suggest, in the face of all this towering achievement, that Ronaldo must produce more than he has done if the accolades showered on him are to be fully justified? The answer lies in the sweep and certainty of those tributes. Everywhere we turn he is being hailed as the best footballer in the world, and there is undoubtedly strength in the arguments supporting the claim. But the careers of the greatest players aren’t defined by persistent excellence in national leagues, though it is an indispensable basis of their status.

The one sure way for a player to have a lasting impact on the imagination of the game’s global audience is by delivering unforgettable performances when competing for the supreme prizes in the most demanding circumstances. Mention of Pele, Diego Maradona, Johan Cruyff or Zidane doesn’t conjure up images from league matches. George Best’s chances of showing the world how marvellous he was were hampered by the limitations of the Northern Ireland team but at 19 he was so spectacularly devastating in United’s annihilation of Benfica in Lisbon that a legend was born. It was permanently embellished when, one week after his 22nd birthday, he supplied the brilliant individual thrust that killed off the same Portuguese club’s resistance in the European Cup final at Wembley in 1968.

For Ronaldo, who turned 23 in February, the most memorable displays in the United shirt have so far come in narrower contexts. He has had good European nights, and their number has obviously increased encouragingly this season, but there has remained a tendency to let slip opportunities to offer a resonant declaration of just how special his gifts are. A recent example was the second leg of the Champions League semi-final against Barcelona at Old Trafford, which imposed a comparison with Lionel Messi. Ronaldo’s industry and commitment were impeccable but as an attacking force he was largely marginalised, whereas every time the hunched figure of Messi was on the ball, manipulating it with magical close-quarters subtlety and shielding it cunningly even when travelling at deadly pace, those of us craving a United victory were desperately grateful for the shortcomings of his teammates. The debate about the best player on the planet was enlivened that night.

Only fools would expect one man to decide this Champions League final (the outcome may hinge on United’s capacity to cope with the smothering energy of Chelsea and especially the fierce physical drive of their midfield) but Cristiano Ronaldo owes it to his talent to have a big say in the proceedings.

Cup romance is alive and kicking

Many of the form upsets that excitingly punctuated this season’s FA Cup could be explained by the reduced commitment, the mercenary priorities, of the country’s strongest clubs. But there was another vital element in the most compelling tales of demise and survival. It was the capacity of some of the outsiders to be galvanised by the opportunities coming from the diluted will of others to the point where they genuinely transcended their normal limitations. Throughout the tournament there was a sense that the cup’s traditional ability to imbue underdogs with irrational self-belief was, however briefly, reasserting itself. And that romantic impression was splendidly sustained in an open, entertaining final at Wembley yesterday as Cardiff resolutely refused to accept the inferiority to which their league position should have doomed them.

They had finished a fairly miserable 12th in the Championship while their opponents, Portsmouth, had claimed eighth place in the Premier League table but this was an afternoon when Cardiff proved that the confident, aggressive, tactically astute football they played to embarrass Middlesbrough in the sixth round was no mere happy aberration. But for a sad goalkeeping error (a stone would have sympathised with Peter Enckelman) they might have had another joyous day.

Nobody could begrudge the winners their celebrations. Portsmouth, after all, can hardly be considered one of the game’s big battalions. This was only their second FA Cup triumph (the other was in 1939) and it was the first time in a long career that a major trophy had been lifted by their gifted and popular manager, Harry Redknapp, who will now lead them into Europe.

For Cardiff this morning there will be only the return to the reality of how distant from a playoff place 12th in the Championship was. The gloom of such thoughts will be deepened by the realisation that, of the two clubs already promoted to the Premier League, West Brom are 11/8 on to go straight back down, and Stoke are 11/4 on.

Murray lost for words

Whatever presents came the way of Andy Murray on the occasion of his 21st birthday last week, we daren’t imagine they included the key to accelerating progress towards fulfilling his (and the nation’s) ambition of providing a credible British challenge in a Grand Slam tennis tournament. That the Scot’s celebrations were blighted on Thursday by a 6-3 6-2 battering from Rafael Nadal was neither a surprise nor a cause for recrimination, given that their third-round meeting at the Hamburg Masters was on the clay surface that is so often a killing ground for the Spaniard. Murray’s career is moving along no better than stutteringly and the wild expectations attached to him when he first emerged on the circuit were long ago tempered by a steady drip of reality. These days he is identified with precocity of the literary rather than the sporting kind. He is publishing an autobiography whose title, Hitting Back, is automatically associated in the minds of many with the chip-on-the-shoulder grumpiness he frequently displays. Few are tempted to give it an on-court application. But perhaps Murray’s retinue of coaches will. They may soon have to resort to the most succinct instruction ever credited to a boxing cornerman: “Retaliate more!”