Five-time major champion Iga Swiatek is being protected by increased security after an "aggressive and taunting" fan verbally abused her at the Miami Open.
Swiatek, 23, was targeted by the man in a practice session on Saturday.
It is believed the man shouted personal insults about Swiatek's family.
The world number two's representatives told BBC Sport the man had previously sent abusive online messages to her through social media.
"The Miami incident appears to be a direct transition from verbal aggression online to harassment in the real world," the Polish player's team said.