England captain Root was heard telling Gabriel ‘there’s nothing wrong with being gay’.
His comments were picked up by stump microphones but Gabriel’s original comments were inaudible but the umpires had a word with him soon after.
BBC’s Test Match Special tweeted: “We understand that West Indies bowler Shannon Gabriel was given an on-field warning about his language by umpires following an incident with Joe Root.”
Root refused to discuss the issue when speaking after the day’s play.
“It’s test cricket and (Shannon) is an emotional guy trying to do everything he can to win a test match. Sometimes people say things on the field that they might regret,” Root said.
“I don’t want anything said in the middle to ruin what’s been a good test series for him and his team.
“He’s a good guy who plays hard cricket and is proud to be in the position he is. The battle was a good contest.”
West Indies’ coach Richard Pybus said he was not aware of what transpired but promised to address the issue if anything “untoward” was said.
At the end of day three, England were 325-4 in the second innings, with a commanding lead of 448 runs with Root and Ben Stokes at the crease.
West Indies lead the three-test series 2-0 after victories in Bridgetown and Antigua.