Saracens' impressive start to the defence of their European title continued with a 44-26 victory over the Scarlets, but there were potentially alarming repercussions for England and Wales.
Maro Itoje was replaced in the 46th minute of a one-sided Champions Cup clash at Allianz Park after rolling awkwardly on to his arm while making a tackle, leaving the 21-year-old lock in discomfort.
In a pitchside interview, Saracens assistant coach Alex Sanderson revealed Itoje had taken a knock to his arm and would need to see a specialist to discover the extent of the damage.
It is a disturbing development for England, who are in the midst of an injury crisis ahead of their autumn campaign that is launched against South Africa at Twickenham on November 12.
Fortune has been at its most cruel in the second and backs rows as only 24 hours earlier Saracens lock George Kruis became the latest victim of the curse sweeping through the Grand Slam champions' ranks when an ankle injury effectively ended his involvement in all four Tests.
The night was every bit as worrying for Wales after full-back Liam Williams limped off early in the first half before being joined in the treatment room by international team-mate Jake Ball, who was grimacing as he clutched his ribs.
Williams has been earmarked for the number 15 jersey against Australia on November 5, while the in-form Ball has been pushing hard for a place in the starting XV.
To add to Welsh woes, Scarlets centre Scott Williams had been ruled out of the trip to London during the build-up because of an ankle problem.
Both clubs' medical teams were kept busy as injured players littered Allianz Park, particularly in the second half, and perhaps an omen of the carnage to come came in the warm-up when Saracens lost skipper Brad Barritt to a stiff neck.
But Barritt's ailment did not prevent the double winners from completing a bonus-point victory that left the outclassed Scarlets in their slipstream throughout.
Mako Vunipola, roaming close to the right touchline, picked up where he had left off in the win against Toulon by running in a dashing solo try that saw him dummy and step his way through the opposition before using his power to surge over.
An overlap opened for Nick Tompkins - Barritt's replacement - after quick hands from Owen Farrell and a defensive error and while the Scarlets scrambled in time on that occasion, their line was breached for a second time in the 26th minute.
There did not appear to be much on when man of the match Tompkins took the ball after a sharp carry from Juan Figallo, but the England Saxon picked a wonderful, arching line that swept him between two red shirts and past Patchell to touch down.
Four penalties from Rhys Patchell kept Scarlets in touch but by half-time the boot of Farrell had accumulated 10 points that helped Saracens establish a 20-12 interval lead.
Daylight opened up between the rivals when Alex Goode launched a counter-attack that was taken on by Mako Vunipola before Farrell flung out a long scoring pass to an unmarked Marcelo Bosch.
Saracens plundered the bonus point when Chris Wyles took Farrell's pass in broken field and raced over in the left corner.
Aaron Shingler crossed for the Scarlets from a clever blindside move, Jonathan Davies added a second before Wyles bagged his brace with five minutes to go of an eventful final half-hour.