The hosts, meanwhile, ended a winless streak of six league games when they defeated VfL Bochum last weekend.
Match preview
Indeed, not many people would have predicted an away win for Freiburg against Bochum, who had only been defeated twice in 12 home games this season prior to kick-off.
Maximilian Eggestein and Michael Gregoritsch both struck either side of half-time to hand their side a healthy two-goal cushion, but Ivan Ordets pulled one back with just under 30 minutes of normal time remaining. Despite generating 24 shots and 60% possession of the ball, though, Bochum could not find an equaliser as Christian Streich's side stood firm.
The victory was even more impressive considering they had defeated last season's UEFA Conference League winners West Ham United less than 72 hours earlier in the last-16 of the Europa League, with Gregoritsch breaking the deadlock after 81 minutes of a cagey encounter.
However, they were thrashed 5-0 at London Stadium in the second leg on Thursday evening, with the Hammers proving far too strong for their opponents. Mohamed Kudus scored a sensational solo goal to seal his side's progression.
Only high-flying Stuttgart have managed to get the better of Freiburg in their last 10 league matches at Europa-Park Stadion, but Streich and his players may be fearing the worst on Sunday considering the relentless form of their forthcoming opponents.
After all, Leverkusen are unbeaten across 37 matches in all competitions this season, with Xabi Alonso's side maintaining their significant 10-point lead at the top of the table by beating Wolfsburg last weekend.
Die Werkself were given a huge helping hand when Moritz Jenz saw red for a second bookable offence after just 28 minutes, with former Southampton winger Nathan Tella making their numerical advantage pay by breaking the deadlock less than 10 minutes later. However, they could not find a second to settle any lingering nerves until Florian Wirtz moved into double figures for the campaign four minutes from time.
Alonso's side had narrowly preserved their unbeaten record when coming from two goals down to draw 2-2 away to Qarabag in Azerbaijan in the first leg of their Europa League last-16 tie, with Patrik Schick equalising in the second minute of injury time.
They were made to seriously sweat by the Azerbaijani champions once again in the second leg at BayArena on Thursday, with Schick sensationally scoring twice in injury time to help his side overturn a two-goal deficit and set up an intriguing quarter-final clash against West Ham.
While Alonso and his players will be desperate to lift a remarkable treble of trophies this season, their priority is almost certainly winning the club's first ever Bundesliga title. Should Bayern Munich win away to rock-bottom SV Darmstadt 98 as expected on Saturday afternoon, the pressure will be ramped up on Leverkusen, who witnessed their title rivals drop points at Freiburg just two weekends ago.
Freiburg Bundesliga form:
L
L
D
L
D
W
Freiburg form (all competitions):
D
W
L
D
W
W
Bayer Leverkusen Bundesliga form:
W
W
W
W
W
W
Bayer Leverkusen form (all competitions):
W
W
W
W
D
W
Team News
Freiburg will have to replace Eggestein, as he received his fifth caution of the season after scoring against Bochum and incurred a one-match suspension as a result. Yannik Keitel is likely to partner Nicolas Hofler in central midfield.
Noah Weisshaupt, Kenneth Schmidt, Max Rosenfelder and Daniel-Kofi Kyereh remain sidelined by injury, but Jordy Makengo and Philipp Lienhart could shake off illness and a groin strain respectively to be named among the substitutes.
Leverkusen will welcome Jeremie Frimpong back to the fold after he missed the victory against Wolfsburg due to suspension. The 23-year-old left a huge offensive void having scored eight league goals from right wing-back this season, so will almost certainly return to the starting XI after scoring in midweek.
However, Victor Boniface remains sidelined by a groin injury, with Jonas Hofmann, Matej Kovar and Arthur also sidelined by muscular issues. Schick should return to the visitors' attack after his heroic exploits from the bench in midweek.
Freiburg possible starting lineup:
Atubolu; Sildillia, Ginter, Gulde, Gunter; Keitel, Hofler; Doan, Grifo; Sallai, Gregoritsch
Bayer Leverkusen possible starting lineup:
Hradecky; Tapsoba, Tah, Hincapie; Frimpong, Xhaka, Palacios, Grimaldo; Tella, Wirtz; Schick
We say: Freiburg 1-2 Bayer Leverkusen
Both teams could be slightly tired having been involved in Europa League action on Thursday evening, but there is little doubt that Leverkusen enjoyed an easier time of things having swatted Qarabag aside on their home turf.
Freiburg rarely lose at home under Streich, but Leverkusen have not lost in any competition all season, and we can envisage them narrowly restoring their healthy cushion at the summit with another victory.