Hungarian tennis player Amarissa Toth said she was "extremely sorry" for her behaviour towards China's Zhang Shuai at the Budapest Open.
Toth, 20, was seen walking towards a contested ball marking and scuffing it out with her foot as Zhang spoke to the umpire.
Zhang retired before completing the first set and left the court in tears.
"I did not think that my first ever WTA main draw success of my career would cause such a storm," Toth said.
"I am extremely sorry for what happened, I respect Zhang Shuai as a player and as a person.