Rugged Roosters prop Mark O'Meley says the rebellious Roosters must bite their tongues in Friday night's NRL derby with South Sydney at Sydney Football Stadium.

The Roosters have suffered three straight defeats, their longest losing streak under coach Brad Fittler, and another hiccup on Friday could drop them out of the top four.

O'Meley pinpointed a lack of discipline as a key factor in the slump.

The Roosters have been on the wrong end of the penalty count for all but a handful of games this year.

"We've got to get back to working together, dominate around the ruck and not give away too many penalties," O'Meley said.

"We've got to be a lot more disciplined than we have and stop putting a lot more pressure on ourselves like we have been."

O'Meley said the Roosters were pinged by referees for a number of reasons and the forwards had been the major culprits.

"It's mainly us forwards, we haven't been square at the marker, or leaving early, or grabbing legs in tackles, we've just got to be disciplined," he added.

O'Meley got into strife with officialdom last week when he was sin-binned by referee Jason Robinson for backchat in the final minutes of the loss to the Sharks.

"I've been a bit frustrated this year with the referees, but that's out of my character, I don't want to be known as Craig Field," O'Meley said, referring to the talkative former Souths halfback.

"So I will probably zip my tongue."

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