Billy Vunipola suffered a knee injury during Saracens' 41-13 demolition of Sale Sharks, while Leicester Tigers and Newcastle Falcons claimed impressive away victories in the Premiership on Saturday.
England back-row Vunipola was sent for a scan after limping out of a one-sided win for the European champions at Allianz Park in the first half.
Vunipola's injury took the gloss off a dominant display from Sarries, who outscored Sale by five tries to two to go top of the table.
Ben Spencer scored touched down in each half and Liam Williams crossed on his home debut early on. Vincent Koch and Nathan Earle also dotted down, with Owen Farrell scoring 16 points from the tee.
Byron McGuigan claimed a second-half double for a Sale, who have won only one of their first four games.
Harlequins entertained Leicester on the back of a fine win at Wasps last Sunday, but they were brought back down to earth by a 31-28 defeat.
Tongan wing Telusa Veainu scored the only try of the first half and Jonny May claimed his fourth of the season for his new club before Greg Bateman went over the whitewash soon after.
It was looking good for Quins when they scored two tries in as many minutes early in the second half courtesy of Danny Care and Mat Luamanu, but George Ford scored 16 points to 11 from Marcus Smith – called up to the England training camp on Friday – as the Tigers edged it.
Newcastle claimed their first victory at the Rec for eight years, scoring five tries in a 33-32 triumph to move up to second.