Reed has lost all three of his games during this week's Presidents Cup
Patrick Reed's caddy was thrown out of the Presidents Cup in Melbourne by the PGA Tour after he "pushed" a fan who verbally abused his player.
The fight came on Saturday after American Reed suffered its third defeat against the international team.
Reed has been postponed all week after being punished for improving the lie of his ball at the Hero World Challenge.
The PGA Tour said, "After an incident, Kessler Karain will not return to caddy for Sunday's singles."
Karain, who is Reed's brother-in-law, had said before: "I don't think there's a caddy I know who would blame me.
" I got out of the cart and pushed it, said a few things, probably a few expletives. Security came and I got back on the cart and left.
"Unless his bones break like Mr. Glass, the most harm done was a little spilled beer, for which I gladly pay him back."
Reed, the Masters champion 2018, had moved sand in a bunker with his practice swing during last week's PGA Tour event in the Bahamas, a violation with a two-stroke penalty.
He has since been criticized by members of the Ernie Els international team, including the Australian. Cameron Smith, who said he "has no sympathy for anyone cheating".
Reed has denied that he cheated and made the light of the incident on Friday by pretending to kick sand after a putt and gestures
He and playing partner Webb Simpson were beaten with 5 and 3 by Hideki Matsuyama and CT Pan while the American team of Tiger Woods lost the morning morning of Saturday 2½-1½.
But the US came four in the afternoon to win 3-1, while the international team had a slim lead of 10-8 ing in Sunday's singles.
"We have been working on it," the American captain Woods told Sky Sports, "We have put down the lead but there are still 12 games to go. We trust each other and we love it.
"I expect my boys to fight, get some red there, get some early speed."
The US needs 7½ points to win an eighth consecutive title while the international team Needs 5½ points to just record a second win in the 13th staging of the Ryder Cup-like event.