World No. 43 Ryan Harrison has been accused of racially abusing fellow American Donald Young during a New York Open match on Monday.
Sixth-seed Harrison was the 6-3, 7-6 victor in Uniondale, New York, and vigorously denies the claims.
"I'm shocked and disappointed, Ryan Harrison, to hear you tell me how you really feel about me as a black tennis player in the middle of our NY match," the 28-year-old Young said on Twitter after the conclusion of the match.
"I thought this was supposed to be an inclusive gentleman's sport."
The pair had argued on-court during the first set and had to be separated by officials.
Harrison responded via the same medium, posting:
"The accusations made by Donald Young tonight following our match are absolutely untrue. I'm extremely disappointed that someone would say this in reaction to a lost tennis match," said the 25-year-old.
"Any video/audio will 100% clear me and I encourage anyone with the available resources to find it."