Flick's announcement capped a turbulent week for Bayern, who bounced back from their Champions League quarter-final exit at the hands of PSG on Tuesday.
Leverkusen stayed sixth, nine points off the Champions League places. Hoffenheim remained 12th. Both teams have had a disappointing start to 2021.
Bosz, 57, has been replaced by former Germany Under-18 coach Wolf, 39, until the end of the season with Leverkusen currently sixth in Germany's top flight.
The latest defeat leaves Leverkusen sixth in the Bundesliga, seven points behind Eintracht Frankfurt in the last place for Champions League qualification.
Bundesliga: Robert Lewandowski's hattrick helps Bayern Munich beat Borussia Dortmund; Hertha Berlin edge Augsburg
Lewandowski completed his hattrick in the last minute, just after Leon Goretzka put Bayern ahead for the first time. Erling Haaland had fired the visitors into an early two-goal lead.
Bundesliga: Bayer Leverkusen continue poor form with loss against Freiburg; Union Berlin held to 1-1 draw at Hoffenheim
Having topped the Bundesliga in December, Leverkusen are now five points adrift of the Champions League places in sixth after winning just one of their last six games.
Leading scorer Luis Suárez has four yellow cards and one more would mean he would miss the next round's derby with Real Madrid.
Bundesliga: RB Leipzig inch closer to Bayern Munich at top with win over Hertha Berlin; Bayer Leverkusen beat Augsburg
A superb second-half strike by defender Nordi Mukiele and a header from centre-back Willi Orban sealed the victory.
Europa League: Manchester United, Tottenham win big in relocated games; Napoli lose to Granada in first leg round of 32
Bruno Fernandes scored twice as Manchester United took a big step toward the last 16 of the Europa League with a 4-0 'away' win over Spanish team Real Sociedad in Italy.
Bundesliga: Erling Haaland spares Borussia Dortmund blushes in Hoffenheim draw; Bayer Leverkusen drop points
Erling Braut Haaland's 81st minute strike averted a fourth defeat in five Bundesliga games for crisis-hit Borussia Dortmund.
Bundesliga: Borussia Dortmund's top-four hopes dented by Freiburg defeat; Bayer Leverkusen thrash Stuttgart
Two goals from Elvis Rexhbeçaj — early in each half — led Cologne over Borussia Mönchengladbach 2-1 in the Rhine derby.
Rot-Weiss Essen struck twice in extra time to knock Leverkusen out with a 2-1 defeat.
European football matchday: Manchester United aim to move level with City in PL; Inter Milan face Juventus in Coppa Italia
In Spain, Sevilla visit second-division Almería looking to make it to the Copa del Rey semi-finals for the first time since 2018, when they lost the title in a final against Barcelona.
Gray, 24, was out of contract at Leicester at the end of the season and has signed for Leverkusen until June 2022 for a reported transfer fee of $2.7 million.
What to watch in European football this weekend: AC Milan wavering; unfinished business for Lionel Messi
A quick look at key points in European football over the weekend across LaLiga, Serie A, Bundesliga and Dutch Eredivisie.
Bayern Munich’s closest challengers, RB Leipzig and Bayer Leverkusen, both lost in the Bundesliga on Saturday to give the eight-time defending champions a chance to move seven points clear at the top.
The victory was Leverkusen's first in five league games and puts them second on goal difference, level on 32 points with RB Leipzig, who host Union Berlin on Wednesday.
There are allegations that Union Berlin defender Florian Huebner racially abused Bayer Leverkusen midfielder Nadiem Amiri, whose parents are from Afghanistan.
For the second consecutive Saturday, Leipzig, who lost 3-1 last weekend at home to Borussia Dortmund, missed out on first place.
Bayer Leverkusen midfielder Nadiem Amiri, who was born in Germany to Afghan parents, was seen having a heated exchange with a group of Union players. Teammate Jonathan Tah later told that Amiri was racially abused.