Original estimates had Surtain missing 4-5 weeks, although that timetable could be adjusted once Surtain begins rehabilitation.
What also is a mystery is exactly when and how Surtain was injured. He left practice early on Thursday and had the knee wrapped in ice, but no one is sure if that was the day the injury actually occurred.
Surtain had complained of soreness in the knee following last Sunday's intrasquad scrimmage, but did not seek treatment.
If anything positive will come out of Surtain's absence, it's that it will give Wannstedt more of a chance to look at young cornerbacks Ben Kelly and Jamar Fletcher, the Dolphins' first-round pick last April.
"It's disappointing anytime a player is going to miss a couple weeks, but we have some young guys who really need the preseason time," Wannstedt said. "We do have five weeks before we play a game."