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.
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.
The injuries 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.
In Ulster's Pool, Clermont defeated French rivals Bordeaux 49-33 in a hugely entertaining Champions Cup clash at Stade Marcel Michelin today.
Bordeaux made a strong start as Jean-Marcel Buttin and Jayden Spence crossed for tries, with Ian Madigan kicking the extra points on each occasion. However, the boot of Morgan Parra limited the damage for the Top 14 leaders as he was successful with three penalties.
Clermont then flexed their muscles with Noa Nakaitaci scoring before half-time, and Parra again adding the extras, to give the hosts the lead before Alexander Lapandry and Wesley Fofana ran in tries and Sebastien Vahaamahina bagged the bonus point.
But Bordeaux claimed a bonus of their own as Buttin posted his second try of the match before setting up Met Talebula, while Gauthier Doubrere scored a late consolation.
Clermont remained top of Pool Five with 10 points after round two and Bordeaux stayed behind them in second spot, for now, with Ulster and Exeter still to play.
Castres ran in five tries in a 41-7 demolition of old European rivals Northampton courtesy of a dominant forward performance that saw the visitors' pack shoved all over the park.
Winger David Smith was the main beneficiary of the hosts' total control up front in the ninth European meeting between the two sides.
He touched down twice - the first a saunter under the posts after captain Alex Tulou's powerful run punched a hole in the Saints' defence after 31 minutes, while his second came four minutes into the second period when he danced past two defenders to score in the corner following a smart offload from Thomas Combezou.
Smith should have notched his hat-trick little more than a minute later, but he was unable to hold on to a sleight-of-hand pass from Tulou with his route to the line clear,
Smith's brace sandwiched a try for loosehead prop Antoine Tichit, who was shoved over the line by his forward colleagues. Benjamin Urdapilleta converted both - the last with a little help from the upright.
Saints had turned down four relatively straightforward penalty chances in favour of kicks to the corner during a period of concerted pressure midway through the first half.
But they were unable to make their possession tell, despite crossing the Castres line. After consulting with the TMO the referee ruled the ball was held up - and the hosts simply shoved the Saints pack off the ball from the resulting five-metre scrum.
It was not the first time the Saints' pack - featuring Courtney Lawes, Tom Wood, Teimana Harrison, Louis Picamoles and the returning Dylan Hartley - had been embarrassed.
The hosts' forwards were on a mission to prove that last week's dismantling at Leinster was an aberration. They pushed the Northampton unit off the ball time and time again. And captain Tulou was causing mayhem whenever he had the ball in hand.
Not even a yellow card for scrum-half Rory Kockott seemed to alter the game plan - or affect their control. In fact, it appeared to galvanise the home side's determination to prove that last week's five-try drubbing by Leinster in Dublin was an aberration.
Northampton arrived seeking their first back-to-back wins over French opposition since 2011/12 following last week's last-gasp win against Montpellier, but in the second half they were consigned to the role of doughty defenders.
They barely broke into Castres territory in the opening quarter of the second half - and even when they managed to get over the gainline, they were held at bay by an organised Castres defence.
The game was long over as a contest by the time Saints' winger James Wilson touched down for a consolation try with eight minutes left on the clock.
There was still time for Castres to notch two more tries. Fittingly, it was a forward who scored the bonus-point try. Replacement flanker Alex Bias charged over in the corner after Northampton ran out of defenders.
And the home fans' celebrations were well under way when 19-year-old replacement scrum-half Antoine Dupont picked up a pass-off-the-floor from man-of-the-match Smith to burst clear for Castres' fifth.