However, the fruits of that work will be on view on Wednesday night in another dear, green place.
It was at the hi-tech home of Real Madrid's second team – which uses recycled water and has solar power providing electricity – that Rodrigo Moreno Machado first caught Coyle's eye. The Bolton Wanderers' manager has spent years cultivating relationships with the Spanish giants in a bid to source emerging talent. Coyle's interest in Rodrigo, though, was matched by Benfica.
The Portuguese club have made a habit of taking young players from Real's academy and polishing them up in Lisbon, while at the same time giving Real first crack at the best players from their own team. That philosophy of never refusing business meant Benfica sold Axel Witsel and Javi Garcia for almost £50 million just days after the draw for the Champions League placed them with Celtic, Barcelona and Spartak Moscow.
The double sale of the midfielders (Witsel fetched £32m from Zenit St Petersburg and Manchester City paid £16m for Garcia) angered Benfica fans, yet manager Jesus Jorge has to be pragmatic. He watched left-back Fabio Coentrao and winger Angel Di Maria sold to Real Madrid in 2010 for a combined fee of £42m, but he knows there is more talent in the pipeline.
So does Coyle. He managed to persuade Benfica to lend Machado – or Rodrigo, as the forward is simply known – to Bolton for a season. However, the Spanish Under-21 player displayed such skill at the Reebok Stadium that it was only a matter of time before Benfica told Jorge to find a place for him.
Last season Rodrigo netted 16 goals in the Liga Sagres and one special volley against Basel in the Champions League. This season, he has scored three in four games for his club and crowned his debut for Spain's Under 21s with a hat-trick last week in the 7-2 defeat of Georgia.
Coyle is convinced Rodrigo has "Galactico" in his DNA and could even return to the Bernabeu one day.
Real's youth academy has provided plenty of graduates who have left the Valdebebas complex outside Madrid and flourished. Chelsea's Juan Mata went to Valencia before his £20m move last year, while Garcia made the same switch to Lisbon as Rodrigo before Roberto Mancini was impressed at his progress last season when he helped suffocate Manchester United's Champions League ambitions.
"I watched Rodrigo when Benfica drew 2-2 at Old Trafford and he was impressive," said Coyle. "Anyone would love to have him at their club. I would never rule Rodrigo out of returning to Real Madrid. There's a lot of player movement between Spain and Portugal and Real keep tabs on their youth academy products and quite often buy them back. They had a buy-back clause in Rodrigo's deal and if he got to the Bernabeu, I have no doubt he will elevate himself to that level. Rodrigo is capable of becoming a Real 'Galactico'.
"We used him as an impact player, coming off the bench, and he was really mature for a boy who was just 19. I had been scouting Real Madrid and Barcelona's B teams a lot then and Rodrigo caught my eye, but was just 17. We tried to buy him when we got Marcos Alonso from Real because I knew he was going to be a top player. However, Real wanted him to be part of the deal when they were buying Di Maria. Benfica paid £5m for Rodrigo, but they felt he was not quite ready and that a year with us in the English Premier League would serve him well.
"In training every day, he was outstanding and showed amazing skills. He managed one goal for us against Wigan and I wanted to bring him back for a second season, but then he scored for Spain in the European Championship under-20 finals and Benfica realised how much he had come on."
It seems like a cruel joke from the football gods that Spain, who have been blessed with so much natural talent of their own, ended up with Rodrigo, too. He was born in Rio, the son of Adalberto Machado, a winger who played for Flamengo in the 1980s. The family moved to Spain nine years ago, to Galicia, where Rodrigo played as a youth for Celta Vigo before moving on to Real Madrid.
"Rodrigo is outstandingly quick, energetic and brave," said Coyle. "He is an unbelievable talent. He moves into places where defenders do not want to go and Celtic's centre-backs do not want to get dragged out wide against him because he has pace and tricks to do you."
Coyle is not convinced Benfica are weaker because of the departures of Witsel and Garcia.
"Benfica have so many quality players coming through that there is no danger of anyone being irreplaceable," he said.
"Their policy is to find emerging players from other markets, to go along with their own youth academy grad-uates, and sell them on. They buy low and sell high. Witsel cost £5m from Standard Liege and they sold him to Zenit for £32m. They also got Javi Garcia for £5m and received £16m from Manchester City. Porto are the same. They have taken in over £300m in the last few years and replaced those players for £40m.
"Benfica like playing against British sides. They went to Chelsea last year in the last 16 and to Old Trafford, but young Rodrigo is in for the experience of his life when he gets to Celtic Park. Champions League nights there produce an atmosphere like no other and I am sure Celtic know all about the boy and can come up with a win."