Lawes, who is in line to challenge for a Lions spot when Britain and Ireland's elite head Down Under in 2013, inflamed his right tibia during England training in Loughborough earlier this week.
The 23-year-old has had a scan to assess the damage and a specialist has advised him to keep his weight of his right leg during the early stages of his recovery.
"It's unfortunate for Courtney as he had just really got back into training with us," said England interim coach Stuart Lancaster.
"But we have to listen to expert medical opinion. If that means he has to keep the weight off his right leg to help him recover then we have to respect that and work with Saints to manage his recovery."
Lawes will initially remain with Northampton for his rehabilitation, with club doctors consulting with the England medical team throughout the process.
Further imaging and scans will then be sort along with more specialist opinion.
And while no timescale has been set for his absence, it would be a major surprise if Lawes returned to action for England's last two tournament clashes against France a week on Sunday and Ireland on March 17.
The news is a second blow in quick succession for Lawes who has only just fought his way back into the England reckoning after tweaking his right knee prior to the start of the Championship.
Having missed the open two fixtures against Scotland and Italy, Lawes played 19 minutes as a replacement in the Twickenham Test with Wales last Saturday.