Ngo was videotaped being punched, kicked and doused with a milkshake by Antifa members during a clash between them and a right-wing group on Saturday in Portland. The footage did not show what led up to the attack or what followed, but there did not appear to be a police presence.
Grenell, a friend of Ngo's, told "America's Newsroom" Tuesday that he believes Antifa targeted Ngo for his political affiliations, as well as his race and sexuality.
"They knew that he is gay, that he's Asian, and that he is conservative," Grenell said.
"We are now in a situation where the largest gay and lesbian groups have stayed silent, not only stayed silent, but their spokeswoman has tried to change it around to say he deserves this," he continued.
The ambassador referred to the Human Rights Campaign, an organization which does not appear to have made a public statement about the attack on Ngo. Their press secretary, Charlotte Clymer, condemned the violence in a tweet to her personal Twitter account, but highlighted Ngo's history as a provocateur.
"Andy Ngo intentionally provokes people on the left to drive his content. Being attacked today on video taken by an actual journalist (because Ngo is definitely not) is the greatest thing that could have happened to his career," she wrote on Sunday.
"Violence is completely wrong, and I find it sad and weak to allow a sniveling weasel like Andy Ngo to get under one's skin like this, but I'm also not going to pretend that this wasn't Ngo's goal from the start," she continued.
Grenell called the comments "completely wrong" and insinuated that the organization is staying silent because Ngo is conservative and of Asian descent.
"This is an organization that demands to have a voice, and if they are not going to use their voice across the board in every situation when a gay person is bashed like this, then they should cease to exist," he said.