Maro Itoje is a doubt for England's autumn series after sustaining an injury to his right hand in Saracens' 44-26 Champions Cup victory over the Scarlets at Allianz Park.
Itoje was replaced in the 46th minute after his arm was trapped awkwardly while making a tackle and the 21-year-old lock is to undergo an x-ray to assess the extent of the damage.
"Maro came off with a sore hand. That needs to be examined and we'll know more after the x-ray has taken place," Saracens director of rugby Mark McCall said.
It is another alarming development for England, who have been decimated by injuries in the build up to their Tests against South Africa, Fiji, Argentina and Australia, stating with the Springboks' visit to Twickenham on Nov. 12.
Openside incumbent James Haskell is out of all four games, while three possible replacements for the Wasps back row in Sam Jones, Mike Williams and Jack Clifford are also sidelined.
Picking Itoje in the No.7 jersey appeared to be the next viable option available to head coach Eddie Jones, but his hand injury could scupper that plan to leave England seeking yet another alternative.
Reigning European player of the year Itoje has been magnificent since making his debut during this year's Six Nations and Jones can ill-afford to lose him.
The injury crisis plumbed fresh depths on Friday when Saracens second row George Kruis underwent surgery on an ankle problem, but McCall revealed he could yet play some part in the autumn.
"George complained about his ankle not feeling great in the week. We had it scanned and there were a couple of loose bodies," McCall said.
"It's a very minor thing, it's just not great timing for anybody. It will be a four to eight week injury. If he plays in the autumn, it all depends if it's good or bad.
"We think the operation went okay and now it all depends on the healing process."