He has not yet had to concern himself with Benfica, as his team do not play them until November, but they, with Porto and Sporting, the other domestic giants, loom large over the game in that country.
Cathro is immersing himself in Portugal and its unique football culture and knows already the scale of the challenge that awaits Celtic tomorrow. He appreciates, also, the big decisions on the mind of Neil Lennon as Benfica arrive in Glasgow. "Benfica have a responsibility to play in a certain way; it's about how Celtic will play," the Dundonian said. "The obvious way is to play deep and try to contain Benfica. Try to protect key zones and have one or two players who can provide an outlet, maybe a player who can dribble for 15 or 20 yards and win some fouls.
"That's the way most people expect Celtic to play. If they do that, they might get something and people [in Europe] will continue to expect the same from Scottish teams – trying to cling on to the glamour of the Champions League. It would be brilliant to see a Scottish team add to that glamour, to go and play against them, be more adventurous in where Benfica start possession. If they start with the ball in your half, with their front four, you might hold out, but you're never going to control the game.
"Why not try to control the phase before that? How good would it be to see Celtic win 3-0 and have 60% of possession? To really make a statement? That's what Scottish football needs. You can play both ways and still lose to Benfica."
This analysis may be depressing for Celtic supporters who envisage their team lining up against Benfica and Spartak Moscow in a race, in all probability, for second place behind Barcelona. Yet even in their home game against Benfica, this is what Portugal expects. And well she might.
Benfica sold two players – Javi Garcia, to Manchester City, and Axel Witsel, to Zenit St Petersburg – for upwards of £49m in recent weeks and still they will field a team packed with internationalists from Portugal, Brazil, Argentina, Uruguay and Paraguay. Portugal has a strong position in the industrial landscape of football, connected historically with South America and linked by geography to Spain, the modern superpower.
"Not having Javi Garcia may not be a problem against Celtic," said Cathro. "He's a big miss in how they balance themselves defensively. When they are starved of possession and have to be more aggressive in deep positions, then yes. With the second sale [Witsel], Benfica sold after the main market had closed. They were happy to put some pressure on the Russians. If they [Zenit] said no, Benfica would be down £35m – if you are in that position then you know you have something.
"Portugal is a preparatory ground for players to become world class. The Brazilian market is a factor. Then there is Spain-Portugal. Players who didn't quite make it there [La Liga] drive through to Portugal and do good work in that league. These are big clubs, they can win the Champions League. They are not going to win it two or three times in a short period, but they have that capacity without being top, top clubs. That leaves that market above the Portuguese league."
Few clubs have sold better than the big two in Portugal. Garcia arrived in England after a £17.5m transfer. Witsel moved to Russia for £32m and Zenit paid Porto the same fee for Hulk, matching the price Atletico Madrid paid for Radamel Falcao.
The Benfica squad still brims with talent. They loaned Nelson Oliveira, the 21-year-old Portugal forward whose game has been likened to that of Eric Cantona, to Deportivo La Coruna. His value will rise if he matures in La Liga, but there was also a need to get him game time that could not be guaranteed at home. "You want him to play in the way you want him to develop," added Cathro of the decision to farm out the prodigy. "Benfica want him to be a leading figure. You don't get that unless you are playing with the pressure of being a reference for the team."
Instead, at the top of the Benfica team is Oscar Cardoza, the Paraguay striker who has been a prolific scorer since he signed five years ago. Now 29, his value is past its peak, but he remains totemic to Benfica. He has twice been Portugal's top scorer, including last season, when he tied with Braga's Lima. Benfica promptly bought the Brazilian – as back-up to Cardoza.
"Benfica is a huge club," added Cathro. "Oscar Cardoza was not going to go to Manchester United or Real Madrid or Barcelona. If the move isn't to that level then, you know, 'I'm playing up front at Benfica – it's a nice life'."
This assessment of Portugal's big clubs, as a perfect breeding ground for talent and a rewarding home for second-tier talents like Cordoza, or declining superstars like Pablo Aimar, the Argentina midfielder, compares as favourably with Scottish football as the markets in which Benfica and Celtic search for their next signings. Celtic's task should not be underestimated.
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