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.