Former Kiwi Addin Fonua-Blake is in strife after calling the referee a "f***ing retard" during a heated NRL match.

Manly forward Fonua-Blake immediately launched a rearguard action by approaching whistler Grant Atkin to apologise, after his team's 12–14 loss to the Newcastle Knights.

And while avoiding direct media questioning, he issued a statement through the Sea Eagles declaring players must respect refereeing decisions.

Fonua-Blake was among the Manly players incensed when they were denied a penalty, or even a penalty try, by bunker referee Jared Maxwell at the end of the match.

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He was sent off for his abuse and faces weeks on the sideline on a likely contrary conduct charge.

In his post-match statement, Fonua-Blake said: "Referees have a very tough job and we all need to respect their decisions even when we may not agree with them.

"I should not have let myself and my club down. That is not who I am or what this club stands for.

"I'd also like to offer my sincere apology to anyone offended by the regrettable language that I used."

Sea Eagles coach Des Hasler said: "From Addin's point of view there was emotion, frustration but you have to contain that. We'll have to wait and see what the charge is and what the fall-out is."

The 24-year-old's abusive burst was heard over the on-field microphones.

Fonua-Blake switched his allegiance to Tonga after playing for the Kiwis in 2017.