Morganella "discriminated against, insulted and violated the dignity of the South Korea football team as well as the South Korean people," Swiss Olympic team chief Gian Gilli said through a translator at a news conference. He said the player was stripped of his Olympic accreditation.
Morganella is the second athlete kicked off a London Olympics team for offensive Twitter comments, following Greek triple jumper Voula Papachristou.
He posted the message after playing in the 2-1 loss against South Korea on Sunday. He said in the tweet that South Koreans "can go burn" and referred to them as a "bunch of mongoloids."
The 23-year-old player later released a contrite statement through the Swiss Olympic team.
"I apologize sincerely to the people of South Korea, to the players, but equally to the Swiss delegation and Swiss football in general. It's clear that I'm accepting the consequences".
"After the disappointing result and the reaction from Korea that followed, I made a huge error."
Officials from the South Korea team declined to comment when asked about Morganella at a scheduled news conference Monday at Wembley Stadium.
But in South Korea, fans condemned his tweet.
Han Sang-min, a college student, welcomed the expulsion of Morganella from the Olympics and called his remark "unthinkable."
"He clearly violates the Olympic spirit. As a soccer fan, I was struck dumb by the way he described South Koreans," he said.
Park Jeong-hwan, a South Korean football fan, said he also was offended.
"I feel like our entire country was looked down upon by the Swiss player," Park said.
Gilli said the player had been "provoked" by comments sent to his Twitter account after the match.
Still, the Swiss team leader acknowledged that Morganella had to be sent home under the terms of the International Olympic Committee's code of conduct, which requires athletes to show mutual respect.
"In this case, we felt we have no alternative," Gilli said.
Swiss media published images of a tweet from Morganella's account (at)morgastoss. The account has since been deleted. The tweet was written in a garbled form of French, appearing to combine a kind of French slang called verlan and text-messaging style.
Swiss officials with the team in Cardiff, Wales, said players were told Morganella was already on his way home.
Gilli said he had tried to contact the head of the South Korean Olympic delegation in London to offer a personal explanation.
"We would like to apologize, especially to the South Korea National Olympic Committee and the South Korea Football Association for the behaviour of the player," he said.
The IOC has encouraged the 10,800 athletes at the London Games to communicate with fans through social media, but it issued guidelines on the standards of behaviour it expected.
Morganella played in Switzerland's first two matches. He received a yellow card against South Korea in Coventry. The Swiss drew 1-1 with Gabon in Newcastle on Thursday. Switzerland plays its final group match against Mexico on Wednesday needing to win by two clear goals to have a chance of advancing to the quarterfinals.
"We have to focus on the game," coach Pierluigi Tami said. "The other stuff (the expulsion) we don't want to think about. Maybe we shouldn't read any newspapers for the next two days."
Morganella made his debut with the senior national team in May and currently plays for the Italian club Palermo.
"We hope that he will draw the necessary lessons for his still young football career," Gilli said.
Last week, Greece Olympic officials tossed Papachristou off the team after she posted a comment mocking African immigrants and supporting a far-right political party.
Associated Press writers Chris Brummitt in Cardiff, Wales, and Sam Kim in Seoul, South Korea, contributed to this report.
Follow Graham Dunbar at www.twitter.com/gdunbarap