Ryan Harrison has protested his innocence after being accused of racism by fellow American tennis player Donald Young.
The pair met in a heated encounter in the first round of the New York Open on Monday night, with the umpire getting down off his chair at one point during the opening set to keep the two men apart.
Harrison eventually won the match 6-3 7-6 (7/4), after which world number 65 Young tweeted: "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. I thought this was supposed to be an inclusive gentleman's sport."
Harrison, ranked 44, quickly responded with a vehement denial of Young's claims.