Ben Te'o has emerged as a fitness concern for England's opening Test with Australia after he missed a key practice session on Monday.
Te'o was forced to miss training ahead of Saturday's showdown at Suncorp Stadium due to "muscle soreness" and watched from the sidelines at the squad's Sanctuary Cove base.
The uncapped 29-year-old rugby league convert is competing with Luther Burrell and Owen Farrell to make his debut at inside centre.
It was first said that Te'o was merely being rested on medical advice, before the diagnosis of muscle soreness was offered along with the hope that he will be able to train on Tuesday.
"It was on the advice of the medical department," defence coach Paul Gustard said.
"He's all good and has settled in really well. He's a good character and gives us something different, adding to our attacking options."
Te'o was the favourite to start outside Owen Farrell, acting as the midfield battering ram in Eddie Jones' 'Bodyline' masterplan that England's head coach believes offers the likeliest route to victory over Australia in the three-Test series.
He has been welcomed into Jones' squad and was given an initiation ceremony at the team hotel on Sunday night which only players, and none of the coaching team, were allowed to attend.
He is famed for his power in attack and defence and Gustard views him as a formidable weapon.
"He's a big, physical guy," Gustard said. "He has the intent to hit people, knock them back and dominate that gainline, control the gainline, the momentum and pace of the ball.
"That's in his DNA and he has that physical intent that most defence coaches like.
"On top of that he's pretty savvy. He's used to playing a channel-based defence in rugby league for the last 10 years of his career.
"He went to Leinster and learnt a different way of defending, so is adept at both systems."
England will name their team to face Australia in the first Test in Brisbane on Thursday morning.