Lance Hohaia has accepted a one-match ban for his forearm strike which sparked the punches from Ben Flower during a brutal opening to Saturday's Super League Grand Final between St Helens and Wigan.
The 31-year-old New Zealand stand-off, who caught Flower off the ball, was knocked to the ground by the Wigan prop's first punch and then lay motionless as Flower landed a second on his face.
Flower will face a Rugby Football League disciplinary tribunal on Tuesday evening charged with a grade F offence, which carries anything from an eight-match ban.
Hohaia was charged with a grade B offence of striking which normally carries a suspension of one or two matches.
Because of his previous record, the St Helens half-back was entitled to submit an early-guilty plea to receive the smallest sanction and avoid a hearing.
"Lance Hohaia has accepted the EGP and will miss the first warm-up game of next season," a St Helens spokesman said.
Flower, 26, can expect a lengthy ban and Saints will await the outcome with interest after meeting with Greater Manchester Police (GMP) about the incident.
St Helens chief executive Mike Rush said: "I can confirm I have spoken to the police but we will allow the RFL to carry out their due process before making any further comment."
A police spokesman said the GMP would also be in touch with the RFL and, if appropriate the Crown Prosecution Service, in order to decide what, if any, action to take.
Rush pointed out that any decision to take legal action would be ultimately be made by Hohaia, who insisted in the immediate aftermath of Saturday's 14-6 win over the Warriors that he bore no grudges against Flower.
Meanwhile, Flower has been defended by his former Wigan team-mate Sam Tomkins.
"It was a surprise," said Tomkins, who played his last match for the Warriors alongside the Wales international in last October's Grand Final win over Warrington.
"It was out of character for Ben. He's a genuinely nice person off the field and I think the heat of the moment it just got to him didn't it?
"He retaliated to being elbowed in the face and took it too far. But Ben put his hand up straight away.
"He was in a bad way straight after the game, he knew he'd let people down, but he's okay. He's got a good family around him and they're all staying with him."
Flower played for Wales in the 2013 World Cup but made himself unavailable for the 2014 European Championship which gets under way on Friday.
Wales' new head coach John Kear said: "Obviously Ben is going to get a hefty suspension because what he did was not acceptable and he realises that.
"You've just got to let the judiciary deal with it and we'll just get on with Wales and the European Championship."