"We're appalled by the fact that an individual, or a couple of individuals, have felt the need to use racist comments to try and emotionally affect a player."
Aca asked to be removed from the field as a result of the abuse, Mr O'Brien said.
"I spoke to him as he came off the field and he was in tears and finding it very difficult to speak."
He said Aca, who joined the team two years ago, ducked off early after the game to spend time with family.
"So it did have an effect on him, but I believe he's a resilient young man."
Canterbury Rugby Football Union community rugby general manager Tim Gilkison said the incident was not the sort of thing the union wanted to see at any rugby fixture.
"We're keen to stamp it out ... [and are] pulling out all the stops to see whether we can identify who it was."
The union had made contact with both clubs, Mr Gilkison said, and its first focus would be on the player affected. "That's terrible for him to have to be subjected to that."
The next focus would be identifying those responsible for the comments, "through any sources that we've got, like footage of that fixture".
The interim vice-chancellor of Lincoln University, Dr John Hay, said a member of the public on the grass embankment was understood to have been responsible for the abuse.
"Lincoln University in no way condones behaviour of this kind."
He said the university would work with the union as well as conducting its own internal investigation.
It had also contacted the Christchurch rugby club to check on Aca's welfare.
"It is always a shame when the ill-considered actions of one person can spoil what is otherwise a great occasion."
