The 54-year-old former footballer told the housemates that he'd be less likely to hang out with Andrew Brady if he and Courtney Act got together.
"Kick them out the club," John declared. "If anything happened in that room [between Andrew and Courtney], he's out of the club. Andrew's out of the club.
"He's not in my club if anything goes on. He's not coming out with me."
Courtney - aka Shane Jenek - later took John to task over his comments.
John put his thoughts down to the "way I was brought up."
He explained: "Things we know that are wrong, we can't help thinking that. Therefore, that is a reality in that I do know it's wrong. I know I shouldn't be that way, but at 54-years-old, I cannot think that naturally."
Explaining being 'uncomfortable' around gay men, John continued: "With gays, they assume he's definitely going to want to have sex with me. That's why men are uncomfortable with gay men. In the back of their minds, they think 'He's looking at me thinking what I look like with my clothes off'."
"It's this uncomfortable feeling that he's going to pounce on me," John added.
The comments not too surprisingly caused anger online.
One viewer wrote: "John Barnes sayin @itsandrewbrady would be “out of the club” and that he would not meet up with him after the show if something happened with @courtneyact is a disgrace. It’s idiots like him that make young men scared to come out #Cbb #cbbuk"
Another added: "John Barnes says his homophobia is okay because he's 54 and he's just naturally homophobic which is possibly the worst reason I've ever heard and so stupid to hear from a black man who campaigned against racism #cbb"
"#cbb No John, that’s lazy. I don’t care if you’re in your 50s. You change with the times or shut up, preferably the former," a third agreed.
And another posted to Twitter: "John Barnes would have been out last night if they’d show that clip before tonight! #cbb #narrowminded
Celebrity Big Brother 2018 airs nightly on Channel 5.