The Newcastle Knights have explained David Klemmer's baffling non selection on Tuesday afternoon, confirming just an hour and a half later that he has been issued a show cause notice in relation to an on-field disciplinary issue.

The club made no further comment on what the issue actually was.

The Newcastle Knights have issued David Klemmer with a show cause notice relating to on-field disciplinary matters in last Sunday’s match against the Canterbury-Bankstown Bulldogs," the club wrote in a short statement.

"No further correspondence will be entered into until the show cause hearing process has been completed."

The Knights fell to the Canterbury Bulldogs at home on Sunday, with more pain heaped on the struggling outfit, and more pressure placed on the shoulders of Adam O'Brien.

According to The Daily Telegraph the show cause notice is in direct relation to Klemmer refusing to come from the field at the end of the game, before also allegedly abusing a trainer trying to inform him he was being substituted out of the contest.

Klemmer has been one of the Knights' best this season, but was linked with a shock move to the Parramatta Eels on the final day of the transfer window yesterday.

The move ultimately never eventuated, however, some reports suggested Klemmer wanted a release from the club altogether - something it was originally reported he wanted when the Knights confirmed the contract extensions of both Daniel and Jacob Saifiti.

Klemmer is on contract with the Knights until the end of the 2023 season as it stands.