Surtain twisted his knee during the afternoon workout and left practice with his knee bandaged and iced. He underwent an MRI Thursday evening.
No official word has been released on the exact nature of the injury, but reports indicate it is torn knee cartilage, an injury that will require surgery. The recovery period is expected to be 4-5 weeks.
Since joining the Dolphins as a second-round pick in 1998, Surtain hasn't missed a game. This injury could force him to miss the Sept. 9 opener at Tennessee.
Second-year cornerback Ben Kelly figures to start in Surtain's place in Monday's preseason opener against St. Louis, although one would expect first-round pick Jamar Fletcher to make a push for the starting job — in Surtain's absence — before too long.
The Dolphins haven't played a preseason game yet, but already have lost offensive tackle Brent Smith (knee) for the season, wide receiver Dedric Ward (foot) for 5-6 weeks, and linebacker Morlon Greenwood for 2-3 weeks (foot).