David Paice and George Robson have both been drafted into England's squad as injury cover for injured duo Dylan Hartley and Courtney Lawes.
The Northampton forwards both went off with knee problems during Saints' 16-6 Aviva Premiership defeat against Saracens at Franklin's Gardens.
England coach Stuart Lancaster has responded by drafting in Paice and the uncapped Robson as Hartley and Lawes's respective problems are assessed.
Northampton rugby director Jim Mallinder did not reveal the extent of both of his players' injuries on Saturday.
"They've done something, but we will know a lot more later," Mallinder said.
"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."
Lancaster's 32-man squad assembled in Burton on Sunday. Their first game is against Fiji on November 10, followed by Twickenham appointments with Australia, South Africa and New Zealand.
London Irish hooker Paice has two Test caps to his name while Harlequins lock Robson will be hoping to impress in the senior set-up for the first time.