Injured Roosters five-eighth Luke Keary.

Short-term pain for potential long-term gain.

That is how Sydney Roosters coach Trent Robinson defended his decision to rest halfback Cooper Cronk against Newcastle at McDonald Jones Stadium on Friday night.

Without Cronk on the field, and after losing likely NSW five-eighth Luke Keary to concussion after just eight minutes, the defending premiers and title favourites were blown away 38-12 by a rampant Knights team.

“They grew the longer the game went. It’s a credit to them,” Robinson said of the Knights at the post-game media conference.

“They’ve been rising over the last few weeks, and I knew they knew this was going to be a test, and they rose again. You’ve got to take your medicine when you have a game like that.”

Robinson explained Cronk was subjected to several days of heavy conditioning earlier this week, to make up for his late start to pre-season training because of shoulder surgery, and the decision to sit him out was made for the long-term benefits of the retiring halfback and the team.

Robinson said the Roosters were “horrible” and “it feels horrible” and “it hurts” after a loss of that magnitude, but he was convinced he made the right decision, disregarding suggestions it could have been interpreted by Newcastle as a sign of arrogance or complacency.

“It was more a respect for all of our squad. It will take 25 players to play how we want to play, and it was a respect for our squad, and it didn’t work tonight,” he said.

“It has worked this year, and it didn’t work tonight, and as I said, that’s on me for that, but you’re not going to change course. I’m not going to all of a sudden run guys into the ground throughout the course of the whole season.”

In his debut for the Roosters, former Knights playmaker Brock Lamb started on the bench but was thrust into the game after Keary was crunched by Daniel Saifiti.

Lamb partnered Latrell Mitchell in the halves but both men had unhappy nights.

“At that point, you’ve still got a half on the bench and you’ve still got a guy that you believe in that can play five-eighth,” Robinson said.

“Obviously right now, you can look at it that way [with regret], but I said I’m not going to walk the path that we’ve all walked to get the same result.

"I know what’s best for the team and it didn’t come off tonight, so a big part of tonight, I’ve got to shoulder the responsibility for that.”

It was Keary’s second concussion in the space of five weeks but Robinson was reluctant to offer an opinion on his playmaker's health or potential to recover in time to play in the June 5 Origin series-opener.

The Roosters have a bye next weekend but, Robinson said, if they had a game scheduled and if Keary passed post-concussion tests and followed the club’s six-day protocol, he would be ruled fit to play.

That would indicate he would be in no doubt to play for NSW in Origin I in Brisbane if he ticked all the relevant boxes with the Blues’ medical staff.