Walker was sent to the bin after playing the ball in the 11th minute and then aiming a kick at stand-in Panthers halfback Jack Cogger at CommBank Stadium on Friday.
The 36-year-old playmaker will learn his fate when the NRL's match review committee issues their charge sheet on Saturday morning.
"It wasn't good enough as a senior player and I've got to be better in those moments not let my aggression get the better of me," Walker said.
"I let my teammates down, and I'm really sorry about that.
"I spoke to Jack after the game and apologised to him, my emotions got the better of me there and it wasn't good enough as a senior player... it's just not on."
Walker's moment of madness will overshadow another incredible tryscoring haul from Penrith winger Thomas Jenkins, who chalked a hat-trick to help the Panthers re-establish a three-win buffer at the top of the ladder.
Jenkins now has 25 tries through 16 appearances this year and is a genuine chance of breaking a 91-year record for the most tries scored in a season, currently held by Dave Brown who crossed 38 times for Easts in 1935.
His treble along with the insatiable output of workhorse fullback Dylan Edwards were critical to the victory as the ladder-leading Panthers snapped a two-game losing streak on Friday.
Edwards chalked up 228m from 20 carries for a Penrith side missing Isaah Yeo, Nathan Cleary and Liam Martin to NSW State of Origin selection..
The Panthers hit the front through a sidestepping Edwards before Walker's sin-binning allowed Penrith to push further ahead through Liam Henry.
Tries for Jennings and Ed Kosi cut the Panthers' halftime lead to 12-10, but some brilliance from Jenkins helped Ivan Cleary's men kick clear in the second half.
The winger climbed high over Jennings to claim a Cogger kick and then fended off Jack Wighton in the corner to grab his first.
"That was pretty impressive and the best thing about the try and halftime that we conceded was, in fairness, probably his error defensively," said Panthers coach Ivan Cleary.
"To be able to put that aside and come back out and have the second half that he did, was that's the most impressive thing - that's a sign of his maturity and development."
His second was much controversial, appearing to have lost control of the ball in the act of grounding. Referee Adam Gee sent it up as a try and with bunker camera angles inconclusive the four-pointer was given.
"I'm over the bunker. I've told you that before," said Souths coach Wayne Bennett.
Billy Phillips barged over next for the Panthers before Jenkins tip-toed down the sideline to touch down for his hat-trick.
The winger's third equalled the record for most tries for Penrith in a season since Rhys Wesser's haul of 25 in 2003.
Cogger was sent to the bin for a high shot on Ashton Ward in the final 10 minutes with Latrell Siegwalt claiming a consolation try for the Bunnies.
6°C