England must decide whether to call up injury cover for Owen Farrell after their captain for the opening rounds of the Guinness Six Nations underwent thumb surgery.
Farrell has undergone a procedure to repair ligament damage and is expected to return to action in seven to 10 days, a timeframe that would enable him to play against Ireland in a fortnight.
However, with England departing for their pre-tournament training camp in Portugal on Wednesday his ability to take part in training could be severely restricted, throwing Eddie Jones' preparations into turmoil.
The worst case scenario would mean he is unable to take part in sessions until four days before the Aviva Stadium title showdown.
"Owen has been complaining - but not very much - about his hand being a bit sore," Saracens director of rugby Mark McCall said.
"We decided yesterday (Friday) to send him for a scan to make sure we know what he's got. We thought he was going to play today and it was after the scan that he was pulled out.
"It turned out to be a very minor problem with a tendon in his thumb. The procedure has already been done this morning.
"As far as I know he'll be back in seven days, something like that, so he should be able to play a full part in the Six Nations.
"I'm sure he will be going to Portugal because I think he'll be available for selection."