While the exact extent of his injury isn't known yet, John Terry has no significant damage to his knee ligaments and will be out for a few weeks, not months.
When John Terry went down during Sunday's match between Chelsea and Liverpool, most feared that he had suffered a long term injury. He was in visible pain and his knee was stabilized before he was stretchered off the pitch, but he's dodged a serious bullet. Chelsea sent out a news release on Monday stating that Terry has sustained 'no significant damage' to his knee, and that he will only miss a few weeks.
Terry recently missed four league games due to suspension, and Roberto Di Matteo won't be happy at his captain's continued lack of availability, but Terry's injury could have been much worse. There is still swelling in his knee that is significant enough that the team can't do an MRI just yet, so he's likely to miss some time, but this is still an excellent stroke of luck for Chelsea.
The very unfortunate piece of news here is that, even though Terry's injury is not nearly as bad as first feared, it could cause him to miss some significant matches. They face Juventus on November 20 and Manchester City on November 25.