The German Football Association (DFB) is investigating Papy Djilobodji after the Chelsea loanee made a throat-cutting gesture in Werder Bremen's 1-1 draw with Mainz.
Match referee Michael Grafe did not see the incident during the game on Saturday, which means it can be reviewed with a view to issuing a retrospective punishment.
"We will investigate the case," Anton Nachreiner, the chairman of the DFB's control board, told kicker.
TV footage showed that the Senegal defender pulled his index finger across his throat while facing Pablo De Blasis after the Mainz attacker went down under Djilobodji's challenge.
Mainz boss Martin Schmidt told reporters after the game: "It was an unfair gesture. You have to do something about it. Those things don't belong on a pitch."
There have been two similar incidents in German football in recent years.
In 2009, St. Pauli player Deniz Naki was suspended for three matches for making the same gesture to Hansa Rostock fans, while Schalke's Gerald Asamoah went unpunished after celebrating a goal in the derby against Borussia Dortmund in similar fashion in 2007.
Bremen coach Viktor Skripnik told reporters after the game: "We'll accept everything that will come. What can I do about it? Papy is a temperamental person. I would have never done that."
Bremen CEO Thomas Eichin, however, defended the 27-year-old.
"I'll speak to him about it and he won't do it in the future, but to me it was a gesture showing the player [De Blasis] he should not play the dying swan."
Saturday's game saw veteran Bremen striker Claudio Pizarro score his 101st league goal for the club to draw level with Marco Bode as the club's all-time leading Bundesliga scorer.
"Claudio wants to score 102 and more goals," Skripnik said after the 37-year-old Chilean, who returned for a third spell last year, converted a penalty.
Bode played for Bremen from 1989 to 2002, helping the club to the 1992-93 Bundesliga title, 1992 Cup Winners' Cup and three DFB Pokal trophies.