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England coach Stuart Lancaster will be sweating over the fitness of Dylan Hartley and Courtney Lawes after both players were forced off in Northampton's loss to Saracens.
The Saints duo were replaced before the start of the second half due to knee injuries, though director of rugby Jim Mallinder did not reveal the full extent of their problems.
Both hooker Hartley and lock Lawes will now be assessed by England's staff this week, with the squad set to meet up on Sunday.
"They've done something, but we will know a lot more later," Northampton boss Mallinder said after his side's 16-6 defeat to Sarries.
"I think Lawes and Hartley are the sort of characters that if they had just got a knock and they will be running around on Monday they wouldn't have come off.
"Courtney tried to carry on, but he was unable to do so. You want them on the field and getting through games. It was disappointing they had to go off."
Mallinder is still hoping the pair recover in time for next week's east midlands derby against Leicester at Welford Road, while Stephen Myler also faces a race to be fit after picking up a hamstring injury.
"Stuart will look to retain his starting 23 and I guess the others will be returned to their clubs," he added.
"It doesn't help when you have two key England lads and Stephen Myler going off with injuries, but I thought in the first half we played pretty well into a big gale, we played some good rugby."