A FIERY on-field exchange involving Magpie Harry O'Brien and Cat Tom Hawkins is not being investigated by the AFL.

The AFL confirmed on Monday umpires had not raised any concerns, and it was simply an on-field matter.

It's understood Collingwood has no issue with O'Brien's behaviour either, and supported the defender's move to publicly clarify the matter.

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A television viewer watching Saturday night's Collingwood-Geelong game took to Twitter, alleging O'Brien called Hawkins a "f***ing f**got". The post was widely re-tweeted and reported.

On Sunday, O'Brien denied he'd used a homophobic slur, but admitted he did direct a spray towards Hawkins.

"Just to clear something up..Id never resort to a homophobic slur..for those wanting to know, I said fat f$@k..simply some onfield banter," O'Brien tweeted to his 44,000 followers.

He continued: "there was a lot of passion in that game & things did get heated...there was 2 way banter...Just what you expect in the heat of the battle."

Last season St Kilda forward Stephen Milne received a $3000 fine from the AFL for directing a homophobic slur at O'Brien.

Matt Thompson is a reporter for AFL Media. Follow him on Twitter @MattThompsonAFL