Young Boys will be hoping to complete the upset when they head to Germany to face Bayer Leverkusen in the second leg on Thursday.
The Swiss leaders are unbeaten in 13 outings following their 2-0 win over Servette on Sunday.
Leverkusen have just three wins in 13 games after they drew 1-1 with Augsburg and sit fifth in the Bundesliga.
Young Boys led 3-0 at halftime in the first leg before Leverkusen pulled it back to 3-3, and then the Swiss side scored a late winner to take a 4-3 lead into the second leg. The German side will need at least a 1-0 win to advance.
The hosts have two wins at home to Swiss teams while Young Boys have three draws and three losses in Germany.
Leverkusen are missing Santiago Arias, Paulinho, Mitchell Weiser, Lukas Hradecky, Karim Bellarabi and Julian Baumgartlinger.
Young Boys will be without Vincent Sierro, Esteban Petignat and Christopher Mathis, while Mohammed Camara and Jean-Pierre Nsame are suspended.
Kickoff is at 3 p.m. EST. on Thursday afternoon at the BayArena. The game will be shown in Canada on DAZN.
Pierre's Footy Talk 