Alexander Zverev, the third-ranked tennis player in the world, was kicked out of the Mexican Open after repeatedly smashing his racket against the umpire's chair.
The incident happened after Zverev and his doubles partner, Marcelo Melo, lost a match.
Zverev was already upset with the umpire over a line call in the final set tiebreaker. He shouted vulgarities at the umpire, calling him an (expletive) "idiot."
In a post on Instagram, Zverev said he regretted his behavior and privately apologized to the chair umpire because his "outburst was wrong and unacceptable."
"As you know, I leave everything on the court," Zverev said. "Yesterday, I left too much."
The German said he will be using the next few days to reflect on his actions to make sure it doesn't happen again.
It's unclear how the ATP will respond to Zverev's threatening behavior.
He is already under investigation for allegations that he physically abused his ex-girlfriend.