Alonso’s side are now on a 17-match unbeaten run after a delayed win in Baku against Qarabag on Thursday made Leverkusen the only Europa League side to have won all four matches at their organisation’s level.
Alonso has a tendency to rotate his team in the Europa League, giving minutes to Robert Andrich, Amine Adli and Nathan Tella, who are all making their Bundesliga debuts. In second gear for most of the game, Leverkusen still controlled to get the 3 points.
Quite the opposite is true this season and the effects and emotions surrounding both clubs couldn’t be more different.
Despite winning their first two Bundesliga games, Union have lost every single league game since then and only ended their previous bad run this week in the Champions League.
Die Eisernen clinched their first Champions League title at Napoli’s cauldron at the Stadio Diego Armando Maradona in a hard-fought draw.
Urs Fischer stopped the rot at Napoli, but Köpenick’s club are winless in thirteen games. From an incredibly tricky position to find three problems to Array Union has a gruelling 90-minute test ahead of it.
Bayer Leverkusen
Alonso will have to do without Brazilian full-back Arthur, who was injured in September while on an overseas U-23 mission. The club have announced that he will be out for around three months, so his return shouldn’t be too far away.
Edmond Tapsoba missed Thursday’s match in Baku and will miss Union’s stop at the BayArena following a hand injury he suffered at Sandhausen at Pokal.
Burkina Faso’s foreign side will be back in action after the international break when Leverkusen visit Werder Bremen.
Czech striker Patrik Schick is still out after suffering another setback in his recovery.
Argentina’s right-hand man Exequiel Palacios is a doubt. He did not travel to Baku on Thursday and Alonso said he wasn’t sure he was fit to play on Sunday, he was feeling better.
Union Berlin
Former Union Berlin player Josip Juranović has returned from injury and is expected to play for the first time in over a month. Club legend Christopher Trimmel has made up for his absence, but Juranović’s return will be welcome.
Rani Khedira is serving a three-match ban he suffered after a foul on Werder Bremen’s Romano Schmid led to a red card for the German midfielder.
Hungarian foreigner András Schäfer has been training on grass, but no return is expected this weekend. The 24-year-old has been suffering from injuries since last season.
Bayer Leverkusen
Hradecký (c); Tah, Kossounou, Hincapié; Frimpong, Andrich, Xhaka, Grimaldo; Hofmann, Wirtz; Boniface
Union Berlin
Rønnow; Bonucci, Knoche, Leite; Král, Juranović, Laïdouni, Haberer, Gosens; Becker (c), Behrens
Florian Wirtz – Bayer Leverkusen
Florian Wirtz now has 3 goals and 4 assists in the Bundesliga for Die Werkself, who pairs perfectly with striker Victor Boniface, who helped Wirtz last weekend against Wolfsburg.
Arguably one of the youngest technically players in the world, the fact that he shines so brilliantly in this incredibly strong and competitive Leverkusen team says it all.
Everything Wirtz does on the pitch comes easy, even though he’s only 20 years old, his influence on matches can’t be underestimated.
The striker has six goals and nine assists in all competitions, but any of those numbers will inevitably increase as the season progresses as he and the club continue to impress.
Wirtz was out for much of last season due to an ACL injury he suffered in March 2022, before pulling off a sensational comeback and regaining his form under Alonso.
He has managed to stay injury-free this season, much to the delight of the Leverkusen faithful. The expectations placed on such young shoulders would weigh heavily on many, but Wirtz takes it all in stride on game day.
Robin Gosens – Union Berlin
Union Berlin made several signings in the summer transfer window, with the aim of bolstering the squad with players with European experience and ability.
The signing of German Robin Gosens looks to be a real coup for Union in their first season in the Champions League, beating VfL Wolfsburg in their signing.
He came off the bench at Napoli and, like many of Union’s new signings, his place in the starting XI was not guaranteed.
His influence on this long-suffering Union side has been remarkable, resulting in four respectable Bundesliga goals from the left-back so far this campaign.
Having enjoyed the Champions League with Atalanta and a final with Inter Milan, his experience will be in navigating the turbulent waters his new team finds itself in.
Where is the fit played?
The match will be played at the BayArena in Leverkusen.
What time is kickoff?
The referee’s whistle will blow on Sunday at 14:30 (GMT).
Where can I watch?
UK audiences can watch the match on the Sky Sports app and website, or on the Sky Sports Mix TV channel with politics at 2:20pm.