The Ronaldo conundrum
Cristiano Ronaldo's astonishing record speaks for itself: 117 goals in 191 appearances for Portugal mean the 37-year-old remains all-but undroppable for Fernando Santos as the 2016 European champions gear up for their challenge in Qatar.
But for all the five-time Ballon d'Or winner's accolades and trophies, for all his success and history-making talent, is a player who has increasingly become a sideshow at Manchester United the answer to the questions that keep popping up around Santos' team?
Ronaldo is certainly going into the World Cup in Qatar out of both form and favour, his club manager Erik ten Hag highlighting time and again that his team perform better without the former Real Madrid and Juventus striker at the sharp end of his side's attack.
While there can be no questioning Ronaldo's remarkable scoring record – his goal against Everton in the Premier League in October was his 700th in club footbal – his growing petulance has the power to undermine any team's internal harmony.
Ten Hag appears to be managing the situation well, highlighting Ronaldo's unavailability for pre-season over the summer as a legitimate reason to keep the Portuguese on the fringes of his team.
The Dutchman demands high standards and the finest conditioning and, by not reporting for duty until late August, Ronaldo has given his manager the excuse needed to keep the veteran sidelined.
United have steadily prospered as a result, with younger, more energetic players such as Marcus Rashford, Antony and Jadon Sancho preferred in attack and Ten Hag's side have improved after a difficult start to the season.
All of that must be galling for a player who has become accustomed to being one of the first names on any team sheet throughout his stellar career. At least, he will think, he has Portugal and the World Cup in November.
But Ronaldo's lack of match sharpness and the absence of trust from his club manager is likely to spill over into the finals in Qatar, when Portugal will justifiably travel to the Gulf with hopes of a run deep into the competition.
Where Ten Hag has excelled is in his management of the Ronaldo issue. He has acknowledged his striker's greatness, pandered publicly to his ego while remaining ruthlessly focused on making decisions that are to the benefit of the team.
The question is: can Santos do something similar?
The veteran coach appeared to take a backseat to his star player during the final of Euro 2016 when the forward looked to be conducting team affairs after leaving the pitch due to injury. No one celebrated the eventual win over France with more gusto than their captain.
But that was six years ago and Portugal have moved on. While Diogo Jota's injury playing for Liverpool will have robbed Santos of at least one attacking option for their group games against South Korea, Uruguay and Ghana, he has others that rival coaches will envy.
Atletico Madrid's Joao Felix has yet to deliver on his promise at international level, but his talent is undoubted. Andre Silva, meanwhile, has started to show his ability with RB Leipzig and has attracted the attention of leading clubs around Europe.
The attacking qualities in Portugal's midfield underlines the class available to Santos. Bernardo Silva's guile is second-to-none and Bruno Fernandes has shown he often performs better, more freely when his Manchester United teammate is not on the pitch.
It's inconceivable, though, that Ronaldo will not be included in Santos' 26-man squad as he seeks the one trophy missing from his remarkable CV. Like his rival Lionel Messi, Qatar is likely to be the last shot at greatness for the strikers who have defined a generation with their record-breaking exploits.
So the onus will fall on Santos to manage the Ronaldo situation, much as Ten Hag has been forced to do at Old Trafford. But is it fair he be asked to soothe the aching ego of a man who should know better? And could Ronaldo's selfish desire undermine Portugal's World Cup challenge?
Numerous World Cup bids have been damaged beyond repair by fractious squads pulling in different directions, undermining the talents that could and should be leading the team to the latter stages of the finals.
France, the defending champions when they turned up in South Korea in 2002, were the ultimate example of a stellar squad torn apart by infighting and injuries, with Roger Lemerre's side crashing out in ignominy at the end of the group phase.
A comparable fate could await the Portuguese should Ronaldo's petulance be allowed to run rampant. For a player who has elevated the game on so many occasions, for one so often lauded for his professionalism and his attention to detail, it would be a sad end to a remarkable career.
Ronaldo's legacy deserves not to be tarnished in such a way and this talented Portuguese squad needs their greatest ever player to accept something he has struggled with so far this season for Manchester United.
Ronaldo has to acknowledge he is no longer the main man, but he can – if he can keep a check on his inherent selfishness – still play a key role for Santos and his country as a team player. To do that he will have to accept, for perhaps the first time in his career, that the world does not revolve around him.