Maro Itoje provided an injury scare for Saracens and England as the European Champions Cup holders made it two wins out of two in Pool 3 with a 44-26 victory over Scarlets on Saturday.
Saracens ran in five tries during a routine triumph, but saw Itoje leave the field with a hand injury sustained in a tackle early in the second half.
George Kruis, a team-mate of Itoje for club and country, is expected to miss all of England's upcoming internationals after undergoing minor ankle surgery. The loss of Itoje would arguably represent an even bigger blow for Sarries and England, given the impact the 21-year-old has made over the last 12 months.
Saracens director of rugby Mark McCall was quoted by the Guardian as saying: "Maro came off with a sore hand. He will be examined tonight and have an X-ray, after which we will know more."
Ulster edged out Exeter Chiefs 19-18 following a thrilling finish to the day's final game at the Kingspan Stadium.
Former Ulster academy product Gareth Steenson looked to have won the game for Exeter with a 76th-minute drop goal, only for Paddy Jackson to respond in kind almost immediately. A last-gasp attempt from Steenson then drifted narrowly wide to ensure the hosts triumphed.
Munster skipper Peter O'Mahony was full of praise for his team after they recorded an emphatic 38-17 victory over Pool 1 rivals Glasgow Warriors, just six days on from the death of head coach and former Ireland international Anthony Foley.
Despite seeing Keith Earls sent off in the first half for a tip-tackle, Munster surged to a bonus-point win on an emotional afternoon at Thomond Park.
"It was a tough day for everyone but I think we got through it as a squad just as Axel [Foley] would have wanted," said O'Mahony.
"We played the way Axel would have wanted and we hope we did him proud. He would have wanted us to play the game and would have wanted us to go out and express ourselves."
In Pool 4, the return of England captain Dylan Hartley failed to inspire Northampton Saints as they suffered their heaviest Champions Cup defeat, a 41-7 trouncing at the hands of Castres at Stade Pierre Antoine.
Top 14 leaders Clermont Auvergne came out in top in a high-scoring Pool 5 clash with Bordeaux-Begles, triumphing 49-33 as both sides claimed bonus points.