United States international Reggie Cannon criticised supporters who booed players for kneeling during the national anthem before FC Dallas played Nashville on Wednesday.
Dallas and Nashville were in MLS action for the first time since March after both teams missed the MLS is Back Tournament due to positive coronavirus tests.
Some fans were allowed into the midweek regular season game, where teams had planned a demonstration in support of the Black Lives Matter movement.
Kneeling before games was a display brought to the public attention by NFL quarterback Colin Kaepernick in the 2016 season, protesting against police brutality and racial inequality. He has not played in the league since.
The demonstration has been repeated around the world across various sports since George Floyd died in police custody in Minneapolis in May.
But jeers were heard among supporters as Dallas, Nashville and the officials took a knee, with a water bottle also appearing to be thrown on the field in response.
Dallas full-back Cannon said after the 1-0 defeat: "I think it was disgusting. I think it was absolutely disgusting.
"You've got fans booing you for people taking a stand for what they believe in, and millions of other people support this cause.
"We discussed with every other team and the league what we were going to do, and we've got fans booing us in our own stadium. How disgraceful is that?
"For a lack of a better word, it p***** me off."
Cannon said the players had asked for the anthem not to be played before the match but "they ignored our wishes".
"We were going to kneel regardless if the anthem was played or not," he explained. "Unfortunately, it was played during the time when we asked for the anthem not to be played."
Cannon, who is black, revealed he had subsequently received an apology from white team-mate Ryan Hollingshead.
"The first thing [Hollingshead] said to me after we got up from the knee was, 'I'm sorry, I'm sorry for our fans'," he said.
"We had someone chanting 'USA' when they don't understand what kneeling means. They don't understand why we are kneeling. They can't see the reason.
"They just think we're the ignorant ones. It's incredibly frustrating."