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Kangaroos prop Paul Vaughan apologised to St George Illawarra teammates and coaching staff for what Dragons mentor Paul McGregor labelled "selfish behaviour" after being stood down for a biosecurity breach on the eve of Thursday night's clash with the Sydney Roosters.

Vaughan will not be available for selection until St George Illawarra's round 15 trip to Brisbane after being ordered to isolate for 14 days for breaching the NRL's COVID-19 restrictions by visiting a café on Thursday morning.

The loss of the Dragons' No.1 middle forward just hours before kick-off against the premiers at WIN Stadium was a massive setback and McGregor said after the 24-16 loss that he was yet to speak with Vaughan about the incident.

"Paul has apologised to the staff and to the group collectively but I haven't spoken to him individually," a frustrated McGregor said.

"We have got a Whatsapp group and I explained the punishment that had been handed to him by the NRL and just concentrated on what we needed to do today.

Frustrated McGregor laments Vaughan's 'selfish behaviour'

"We're well aware of what our responsibilities are. We talk about it consistently so there is no reason for it expect selfish behaviour.

"It's not what you need from one of your senior players and someone who is important to your footy team."

The Dragons promoted Josh Kerr into the starting line-up and called up new recruit Kaide Ellis for his first match since the NRL season resumed on May 28 to accommodate the loss of Vaughan.

Match Highlights: Dragons v Roosters

"I spoke to the guys in the Whatsapp, said to let it go now and concentrate on what we have to do tonight and we will discuss it at a later point," McGregor said.

"We spoke about whatever it takes and how everyone needs to be doing the right thing by one another and the game. Everyone has got to make some sacrifices and that is one of them.

"The game has done well to get back going so we have got to be respectful of that."

There was further bad news for the Dragons, with NSW Origin second-rower Tariq Sims coming from the field early in the second half with a shoulder injury.

McGregor admitted there was concern about the extent of the injury, while lock Jackson Ford was placed on report for tripping Roosters playmaker Luke Keary as he crossed for his side's last try.