Stuttgart, meanwhile, can move into the top half of the table with a victory.
Indeed, after looking like challenging Bayern Munich for the title prior to the winter break, Leverkusen have dramatically fallen away in recent weeks.
Leipzig could have scored more goals themselves, though, with Marcel Sabitzer's opener disallowed for offside and the midfielder striking the bar from distance late on. The winner came via Christopher Nkunku's brilliant touch and strike past Lukas Hradecky, with Alexander Sorloth hitting the post moments later.
Things went from bad to worse for Leverkusen in midweek with an embarrassing 2-1 defeat to Rot-Weiss Essen in the DFB-Pokal after extra time. The fourth-tier side held Bosz's side to a goalless draw after normal time, with Leon Bailey's strike moments before the half-time interval of extra time looking like sinking RWE's hearts.
However, Oguzhan Kefkir and Simon Engelmann both struck to produce a historically incredible comeback and victory, with Leverkusen's morale now surely at an all-time low heading into the game against Stuttgart on Saturday.
Stuttgart, meanwhile, were buoyed by finally recording their first home win of the season with a comfortable 2-0 victory over struggling Mainz 05.
An interesting but goalless first half burst into the life after the break, with Borna Sosa's gorgeous cross headed home by Sasa Kalajdzic to open the scoring. Silas Wamangituka highlighted his phenomenal quality to seal a crucial three points for Stuttgart, running from his own penalty area before cutting inside Mainz's half-hearted defenders and firing into the near post.
Wamangituka was at it again in midweek by scoring after only two minutes in the DFB-Pokal third round home tie against Borussia Monchengladbach, but strikes from Marcus Thuram and Alassane Plea either side of half time saw Stuttgart disappointingly crash out of the competition.
However, given that Pellegrino Matarazzo's side have won half of their 10 away matches this season, they will have every confidence of pouring further misery on Leverkusen on Sunday, and they may look to blitz them from the outset.
Bayer Leverkusen Bundesliga form: LDLWLL
Bayer Leverkusen form (all competitions): WLWLLL
Stuttgart Bundesliga form: LWDLLW
Stuttgart form (all competitions): WDLLW
Stuttgart, meanwhile, suffered the blow of losing Gonzalo Castro to a hamstring injury in the win over Mainz, with the midfielder likely to miss the rest of February.
Bayer Leverkusen possible starting lineup:
Hradecky; Fosu-Mensah, Tah, Tapsoba, Wendell; Sinkgraven, Demirbay, Aranguiz; Bellarabi, Alario, Wirtz
Stuttgart possible starting lineup:
Kobel; Mavropanos, Anton, Kempf; Coulibaly, Endo, Mangala, Sosa; Wamangituka, Gonzalez; Kalajdzic
We say: Bayer Leverkusen 1-3 Stuttgart
With Leverkusen potentially missing a whole host of first-team options, we can envisage Stuttgart blowing the hosts away.
The absence of Castro will be a blow, but the likes of Wamangituka and Nicolas Gonzalez could be too hot for Leverkusen to handle in their current crisis of confidence.