Although his club will not identify a recovery timescale, it appears unlikely he will be available for the November 5 clash against New Zealand at Twickenham. England then face
Argentina and South Africa (twice) on successive weekends.
Borthwick, capped 27 times, is a key member of England head coach Andy Robinson's plans this season and heading into the World Cup defence next year.
He started all of England's RBS 6 Nations Championship games last term, and his possible absence in November will come as a huge blow to Robinson.
Borthwick's second-row partnership - for club and country - with Danny Grewcock is rated among the most prolific in European rugby, although World Cup-winning Leicester lock Ben Kay is gradually recapturing top form and will undoubtedly challenge strongly to make England's starting XV.
Seven of Robinson's 41-man elite player squad - Harry Ellis, James Simpson-Daniel, Mathew Tait, Mike Tindall, Mark Van Gisbergen, Lawrence Dallaglio and Phil Vickery - have yet to start a match this season because of varying injuries.
And four more squad members - Borthwick, Jonny Wilkinson, Michael Lipman and Iain Balshaw - are currently sidelined after starting the Premiership campaign on schedule.
"He (Borthwick) needs time from a recuperation point of view where it is total rest, and the situation will then be reassessed," said Bath's acting head coach Steve Meehan.
"The first two weeks are quite important to his overall recovery, and after that period, when an examination will take place, we will then have a fair idea about when to expect him back.
"He had a slight ligament tear that had to be repaired. I cannot give any times of a comeback at this moment."