Owen Farrell and George Kruis are both injury concerns for Saracens' Champions Cup quarter-final against Leinster next Sunday.
The British and Irish Lions duo both sat out Saracens' 24-11 win over Harlequins on Saturday, with Alex Lozowski playing at No 10 and kicking 14 points in Farrell's absence.
Kruis was taken off after 71 minutes of England's 24-15 loss to Ireland, while Farrell played the entire match, but Saracens director of rugby Mark McCall confirmed both players picked up injuries.
"We hope he (Farrell) will be [fit] but there's no guarantee," McCall said. "He's got a quad injury, it's a muscle injury and you never really know with these things.
"George Kruis has got a back injury, it is what it is and we will deal with what we have to do next week."
Billy Vunipola is also facing a "race against time" to be fit for the trip to Dublin as he continues his recovery from a fractured arm in January.
One player who will be fit to face Leinster is Maro Itoje, who scored a try in the win over Quins.
McCall feels the England lock provided the perfect answer to recent suggestions by Sir Clive Woodward that Itoje looked "out on his feet" against Ireland.
"Maro was brilliant and looked like he was full of energy, full of life and he was deservedly man of the match," he said.
"It will give him a lot of confidence going into next weekend, but his performance wasn't a surprise to us.
"Sometimes when people tell you that you look tired then you can feel tired, but Maro is not that kind of individual and I think he proved that."