Only when the game is over and the proceedings concluded will we be able to give an educated assessment of Rayos Del Necaxa, Manchester United's first opponents tonight.
At the moment they are an unseen quantity to most of us and we must rely on reports from their previous gallops.
Fortunately for United, Alex Ferguson does not need to rely on hearsay, having watched the Mexicans on video, although his analysis was hardly fully formed. "It's difficult to tell what they're like," was Ferguson's opening line, "but they are big and tough at the back and they have a pattern."
Imagine one of Ferguson's scouts writing something similarly vague. It was a more informative experience listening to the opinion of Necaxa's best player and their captain, Alex Aguinaga.
Aguinaga is an experienced and gifted midfield playmaker and after training in Rio on Tuesday night he spoke about his team-mates. Their strength, he said, "is the union of our players. There are old and young and we are all together. We don't fear Manchester United, we respect them. We are not scared. In Agustin Delgado we have a jewel."
Like Aguinaga, Delgado is from Ecuador, but at 25 is six years younger than his captain and is said to have been unsettled by recent transfer speculation. He is Necaxa's main striker and scored 11 goals in 19 games before the Mexican league's winter break. Necaxa, whose game is naturally defensive, tend to search for Delgado on the counter-attack. It should represent nothing too shocking to Jaap Stam.
Their other principal striker is a Uruguayan, Sergio Vasquez, who scored the winning goal in the Concacaf play-off that brought Necaxa here. The game, against Alajuela of Costa Rica, was played in Las Vegas in front of a tiny crowd and the only factor of that experience likely to be of relevance tonight is that in Las Vegas the temperature was 101 degrees.
When the contrast of facing Manchester United in the Maracana was put to manager Raul Arias he replied: "We're not worried about the Maracana. We play in the Azteca." That is true but the magnificent stadium in Mexico City is akin to Selhurst Park when Wimbledon are entertaining unfashionable opposition. The Wimbledon comparison has further credence given that Necaxa, the smallest club in their city, are resilient and have continually over-achieved.
Like United in England, Necaxa are Mexico's team of the Nineties, collecting three league titles, losing two cup finals and appearing in nine of their league's play-offs. As such they deserve respect, although the Mexican league is of dubious repute - last season a relegated club, Puebla, bought the franchise of a promoted club, Union de Curtidores, who would have passed them on the way up otherwise.
Within the country Necaxa are viewed as having the chance to show how strong the Mexican League is and Arias is nothing if not bullish about that prospect. "I cannot minimise the importance of Manchester United, a team I respect," Arias said. "But they can be beaten, as can South Melbourne and Vasco da Gama."
