The Senegalese forward approached Sane in the dressing room after the two playmakers were seen bickering on the field. The blow left the German winger with a bloody lip before teammates intervened to break up the fight.
The former Sky Blue Sane proved to be Bayern's primary offensive weapon that night, contributing to each of their four attempts on goal.
Conversely, Mane returned to English grounds and took a spot on the bench. Despite his 20-minute stint on the field, he failed to make a noteworthy impact.
Mane: Passionate or reckless?
The 31-year-old Mane may face a fine for his belligerence which accentuated a poor night for the Bavarian giants. The club is unlikely to progress from the quarter-finals before the second leg next Wednesday.
In addition to the considerable three-goal disadvantage, newly hired coach Thomas Tuchel now faces the challenge of addressing internal conflict.
“FC Bayern cannot accept that. It will go beyond a fine. The club has to set an example,” said Sky Reporter Florian Plettenberg.
“With Tuchel, they brought in a coach under whom things like that shouldn't happen. I don't think Sadio Mané has a future at Bayern beyond the summer.”
With tension murmuring following the incident, Sadio Mane left in a private car upon landing in Munich. Mane took the bus with the rest of the team.
The Bundesliga front-runners face off against Hoffenheim on Saturday.