PORT Adelaide has failed to downgrade Dan Houston's five-match ban at the AFL Appeals Board, meaning the star defender's season is now over.

The suspension means the All-Australian defender will miss all of the finals series, even if Port makes it to the last Saturday in September.

A remorseful Houston pleaded guilty to rough conduct at the Tribunal on Tuesday night for his brutal bump on Adelaide's Izak Rankine.

The Power, who argued for a three-match ban, launched an appeal when the Tribunal handed down the five-match suspension.

In what became an at-times feisty appeal on Thursday night, Port Adelaide's counsel Paul Ehrlich argued there was a failure of procedural fairness and the Tribunal's finding was simply wrong as a matter of law.

Ehrlich argued that Tuesday's hearing was not conducted on the basis that Houston breached his duty of care in his decision to bump.

"The expression does not appear in the transcript until mentioning the Tribunal reasons," Ehrlich said.

"The AFL did not allege or submit that he breached any care by electing to bump instead of electing to tackle.

"The AFL said the bump would have been permitted save for the high contact.

"It's not a breach of duty to make an election between two lawful rights under the laws of the game.

"Yes he can tackle, yes he can bump. He chose to bump, and that decision was not a breach of duty.

"We say there was a denial of procedural fairness. It's an error of principle."

Port Adelaide also argued Houston's exemplary record wasn't fully taken into consideration, and the five-match ban was grossly above what should have been reasonably handed out.

"What the tribunal has done on penalty is take into account the potential for more serious injury," Ehrlich said.

"We say that's an error of law."

The Power also disputed whether there had in fact been contact to the neck or the top of the shoulder during the bump.

Appeals board chair Will Houghton questioned several of Ehrlich's arguments, with the pair agreeing to disagree at times.

Lisa Hannon, representing the AFL, said the Tribunal had been fair and reasonable in reaching its verdict of five matches.

"There was ample evidence to suggest contact to the top of the shoulder," Hannon said.

"We utterly reject that contention (of breach of procedural fairness)."

The Appeals Board knocked down all of Port's arguments, dismissing the appeal.

"In our view, none of the matters that Houston raised would relate to any error of law that the tribunal was said to have made," Houghton said after reaching his decision.

"They relate to factual findings by the tribunal.

"The penalty imposed is not plainly outside of the range of penalties available."

Houston is unlikely to return to Alberton next year, with a return to his native Victoria well and truly on the cards.

The 27-year-old didn't speak at the Appeals hearing, but he expressed his remorse on Tuesday night.

"I regret my decision to bump Izak, and I'm very sorry for the injury my decision caused," Houston said.

"I never meant to hurt Izak, let alone concuss him," Houston said.

"I don't know why I didn't tackle. In the past this has been my first instinct. I don't know why I decided to bump because I can't remember making that decision because it all happened so quickly."