RB Leipzig coach Ralph Hasenhuttl refused to shake hands with Daniel Baier after the Augsburg captain made an obscene gesture in his direction when the two sides met on Tuesday.
With around 15 minutes left and hosts Augsburg defending a 1-0 lead, midfielder Baier went to ground close to the Leipzig technical area.
As he got up, he made an obscene gesture in the direction of Hasenhuttl and also appeared to spit in his direction.
The Leipzig coach told Sky: "I don't need to comment on it. I informed the officials but they did not see it, otherwise he'd surely have been thrown off the pitch."
Baier, however, played down the incident, saying: "That was a 90-minute battle, and you might do things which are a bit emotional.
"I let myself get carried away."
The player was backed by Augsburg sporting director Stefan Reuter, who told reporters: "It was emotional. You should forget this scene -- that's all I will say about this."
The club's president, Klaus Hofmann, meanwhile, hit out at Leipzig in Bild, calling them "bad losers" and "arrogant."
The German FA (DFB) confirmed to publications including kicker that it has opened an investigation into Baier, who was not punished by referee Daniel Siebert.