Port Adelaide coach Matthew Primus refuses to detail the disciplinary breach that has cost troubled forward Daniel Motlop a spot for their AFL season opener.

Motlop, who last year was offered for trade, has been overlooked for selection for Port's away fixture against Collingwood on Saturday.

Primus confirmed the non-selection of the gifted goalsneak was for disciplinary reasons, but refused to reveal specifics.

"That is in-house," Primus told reporters on Friday.

"The players and the leadership group have set standards of what your preparation is going to be during a week of footy.

"And since Daniel hurt his ankle last week it hasn't been up to those standards.

"The leadership group and the match committee thought not living up to those standards, that is the reason he wasn't picked for this week.

"So he'll play for (SANFL club) North Adelaide and rectify that and try and get back into our team."

Motlop is due to stand trial next month on a charge of assaulting the girlfriend of teammate Jacob Surjan, who will also miss the Collingwood match due to injury.

The 29-year-old Motlop was touted for trade last year after injury and poor form restricted him to just nine games.

But the mercurial talent had been a standout performer during Port's preseason in his bid to make amends.

"He has been terrific this preseason, he has trained well, he's been in good form for us as a player," Primus said.

"It's just the standards that the leadership group and the coaches and all the playing group want to set, and he hasn't quite lived up to that."

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