St George Illawarra coach Paul McGregor has warned of changes to his side after Newcastle fully exposed a frailty in the Dragons this season that has been masked by recent strong first half performances.

The Dragons trailed 28-0 at half-time before being thumped 45-12 in Mudgee on Sunday and McGregor believes the heavy defeat may have been a while coming after the second-half collapses against Parramatta and the Warriors in the past two weeks.

A disappointed McGregor said his middle forwards had become frustrated after repeated errors by teammates and he would look at changes for next Sunday’s match against Cronulla at WIN Stadium in a bid to end the club’s four-match losing streak.

"I think for the first 40 minutes we didn’t show any resilience in defending errors or penalties, which is highly disappointing," McGregor said.

"I feel that the frustration was starting to come from some middle players on the footy field through those errors and us not defending tackle-five kicks and shifts.

"We've got to have a real good look at why. Up until today, our first 40 minutes has been like a top-four side and our last 40 minutes has been like a bottom-four side.

"The same people are making the same errors and the poor reads on a weekly basis so it might be time for change.

"Right now, we're halfway through the year so if we're still making the same errors, and giving away the same sort of penalties, the same people are doing it that means they're not listening."

McGregor’s options are limited but he confirmed lock Korbin Sims would be available for the match against the Sharks after recovering from a broken arm. Five-eighth Corey Norman is likely to return from a fractured cheekbone in the following match two weeks later.

Veteran forward Jeremy Latimore was ruled out of the Knights clash after aggravating a knee injury at training and McGregor said he would be sidelined for another two weeks, while the Dragons had expected Jack de Belin to play if he won his legal challenge to the NRL’s "no-fault stand down" policy.

The Australian Federal Court decision against de Belin last Friday rocked some of his teammates and McGregor conceded it may have been a distraction leading into Sunday’s match.

"I hope that didn't have an effect on the performance today, some say it may have because Jack is a very well-liked person and an important part of our football team," McGregor said.

"To be totally honest we all expected him to be available today, but he wasn't so we had to move on pretty quickly from that.

Dragons: Round 10

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"There's feeling there, there's definitely emotion there for sure. Whether that played a role in today's performance or even in my build-up, I'm not sure subconsciously. Certainly he is a big part of our lives.

"But he wasn't there today and there 17 players and coaching staff who didn't do what they needed to do."

Asked if he would consider removing de Belin from the senior training squad if he was unable to play, McGregor said: "He's a part of our club and a part of our team. He's got the assumption of innocence until he gets his opportunity in court."