THEY have lost the inspirational manager who led them from the second tier of Belgian football to the brink of the title in the space of two seasons to Anderlecht.
The striker who plundered 27 goals in all competitions in the 2021/22 campaign has also moved on to Premier League outfit Brighton following a £5m transfer.
And only yesterday the midfield lynchpin who was so integral to their improbable success last term completed a £4.5m switch to Club Brugge.
They have, too, an average attendance of just 5,854 at their home games and have never featured in Europe’s premier club competition before in their 124 year existence.
But nobody in Belgium is writing off Royale Union Saint-Gilloise’s chances of beating Rangers in the Champions League third qualifying round next month and joining the likes of Bayern Munich, Manchester City and Real Madrid in the lucrative group stages.
The tiny club based in the outskirts of capital city Brussels have a long and proud history – they were crowned national champions on 11 occasions before the Second World War.
However, they had spent no fewer than 49 years outwith the top flight when they won the Challenger Pro League and a long-awaited promotion last year.
So their success in the Jupiler Pro League last season – they topped the regular season table by five points before being pipped by Brugge in the play-offs – was completely unexpected.
Bart Fiermans covers Union for Belgian newspaper Het Laatste Nieuws and was taken aback by their performances against giants like Brugge, Anderlecht and Royal Antwerp.
“Nobody thought they would be contenders for the title,” he said. “They didn’t have a big budget and hadn’t been in the top league for a long time. But it was like stepping into a time machine and going back to when they were dominant side in the country.
“They had a good group of players with a great team spirit and a clever coach in charge. They almost succeeded in doing what Nottingham Forest did in England in 1978 by winning the title in the first season after they were promoted.
“They finished five points clear after the regular season, but Club Brugge went above them in the play-off games and lifted the league. When they lost to Brugge in Bruges the players had tears in their eyes.”
Fiermans added: “Felice Mazzu was an experienced and tactically astute manager, but he was also a great motivator, a good people person. He did a great job during his time in charge.
“Mazzu’s team played very defensively, but broke quickly towards goal on the counter attack. That was the reason for their success. They executed their style of play very well.
“They had two brilliant strikers, Dante Vanzeir and Deniz Undav, who really complemented each other. When they had space and got on the ball they were lethal. They scored a lot of goals and provided a lot of assists.
“The other important player they had was Casper Neilson. The Dane was the defensive midfielder and was the brain of the team. He was very, very good.
“In defence, they had Christian Burgess, the English centre half, who was a very solid defender. He was the rock of the side.
“Anthony Moris, the Luxembourgian keeper, also had a good season. He had the most clean sheets in the league, one more than Simeon Mignolet of Brugge.”
Union have since been victims of their success; Mazzu has moved on to Anderlecht and been replaced by his assistant Karel Geraerts, Undav has departed for Brighton and Neilsen has just joined Brugge.
Will they be able to scale the same heights in the coming weeks and months and overcome the Europa League finalists in Champions League qualifying without that important trio? Fiermans is unsure how they will fare.
“Mazzu has moved on to Anderlecht, a bigger club,” he said. “His assistant, Geraerts, has taken over as head coach.
“Undav has gone to Brighton. Union are trying to find a striker who is similar to him, but that will not be easy. Neilson has just been transferred to Brugge this week for €5.5m.
“Geraerts has stated that he will not make big changes and will retain the 3-5-2 system which his predecessor favoured. He will have his own thoughts, but he will not oversee a big transformation. That will help him to maintain their form.”
Fiermans continued: “Union played in Europe in the 1950s and the 1960s against clubs like Roma, Juventus, Marseille and Hearts on one occasion as well. They reached the semi-finals of the Inter-Cities Fairs Cup once.
“But they had not played in the top division for 49 years before last season. This is the first time in 58 years they have played in Europe. It is really remarkable.
“Union supporters think it is like a fairytale. To be back in Europe and to have a chance of qualifying for the Champions League is unbelievable. They are happy to have drawn a big name like Glasgow Rangers.
“It is very difficult to predict how Union will get on this season because Undav and Nielson have gone and Geraerts has taken over as manager. On paper, Rangers will be too good for Union.”
Union - who have been resurrected since being taken over by Tony Bloom, the English professional gambler, and Alex Muzio back in 2018 – play in the iconic Joseph Marien Stadium.
Fiermans, though, expects the Rangers match to be moved to the Den Dreef, the home of their local rivals OH Leuven, for the Champions League qualifying tie.
“The Union stadium is amazing,” he said. “The stadium is exactly the same as it was before the war. It has an art deco façade and is a protected building. They are not allowed to change it. It has great charm and authenticity.
“The club are well liked in Belgium. Their supporters are very friendly. They don’t make negative comments, there is no aggression at all, they are pacifists.
“They also get a lot of supporters from other countries, ground hoppers who want to visit the club. They get a lot of hipsters, young people who go to the stadium to sample of unique atmosphere.
“Unfortunately, they can’t play their European matches there because it is not up to UEFA standards. They will probably played at Leuven’s ground. It is not too far away and they have played games there before.
“Union played Feyenoord in a pre-season friendly in Rotterdam at the weekend and they won 4-0. Okay, it was not a competitive fixture, but to beat a club like that by that much away from home is not bad is it?”
