Down for the count: Kalyn Ponga has required seven HIAs in his past 18 games

Ponga was knocked senseless less than two minutes into Sunday's remarkable 14-12 win against Wests Tigers at Leichhardt Oval after a sickening head clash with Tigers back-rower Asu Kepaoa.

After crashing to the turf, he was helped from the field and played no further part in proceedings.

He has been ruled out of Friday's clash with the Dolphins at McDonald Jones Stadium and it remains to be seen how long he will be sidelined before he is again considered for selection.

"It's too early to say," Knights coach Adam O'Brien said after Sunday's game. "We'll just follow the protocols ... we'll just follow the guidelines. He obviously won't play [against the Dolphins].

"We've got a five-day turnaround to patch that group up, so he's not going to be a part of that."

The 24-year-old Queensland Origin representative needed five HIAs last year - prompting the Knights to stand him down for the final six games of their campaign - and he underwent at least another five assessments in the preceding four seasons.

In Newcastle's two games this year, he was controversially ordered off for a HIA in the round-one loss against the Warriors and was then clearly dazed after his collision with Kepaoa on Sunday.

In most of those instances, Ponga was either cleared to resume playing in the same game, or backed up to play the following week.

But now concern is mounting for the long-term future of the highest-paid player in the Knights' history.

O'Brien said after Sunday's game that Ponga had been given an "extended break" over the summer, and the club opted not to select him for the final round last season, even though he had been given a clearance to resume.

He also declared himself unavailable for selection at the end-of-season World Cup, although there is no guarantee he would have been selected by Kangaroos coach Mal Meninga.

He is now expected to face a battery of neurological tests as specialists try to determine how much time he needs to recover before he can return to the firing line.

O'Brien said Ponga and co-captain Jayden Brailey, who was also replaced against the Tigers after suffering a concussion, were both "up and about [in the dressing room], which is a good sign for us."

In recent seasons, a host of high-profile NRL players have been forced to retire prematurely after being repeatedly concussed.

Former Sydney Roosters forwards Boyd Cordner and Jake Friend both gave the game away because of concerns about their long-term health and welfare.

Ex-Knights James McManus and Tim Glasby were also forced to call it quits because of the after-effects of multiple concussions.

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