After LeBron James called United States president Donald Trump a "bum", Cleveland Cavaliers owner Dan Gilbert said he received several racist voicemails.
During an interview on CNBC, Gilbert said he did not realise how prevalent racism was in the United States.
"I received voicemails after LeBron tweeted that were some of the most vile, disgusting, racist [messages]," Gilbert said, via ESPN.
"There's an element of racism that I didn't even realise existed in this country this much."
The James tweet came after Trump said NBA champions the Golden State Warriors were not welcome at the White House.
U bum @StephenCurry30 already said he ain't going! So therefore ain't no invite. Going to White House was a great honor until you showed up!-- LeBron James (@KingJames) September 23, 2017
But Trump's announcement came after Warriors guard Stephen Curry said the team would not visit the White House even if invited.
"The thing is, I mean, some of the most disgusting things I've ever heard people say," Gilbert said.
"And you could hear it in their voice - the racism. It wasn't even really about the issue, and that's what really got me because they went to who they really are, some of them."