We mentioned in today's notebook that rookie Chris Cook is expected to start at right cornerback Saturday in the third preseason game against Seattle.

That is a pretty significant development, which shows the coaching staff is giving serious consideration to opening the season with Cook as the starter opposite Antoine Winfield.

Cook got most of his work in camp behind Winfield on the left side and initially the coaches wanted to keep him strictly at that spot. It appeared that one or a combination of Lito Sheppard, Benny Sapp and Asher Allen would hold down the right side until Cedric Griffin is healthy enough to return from his knee injury.

But Cook has impressed the coaches to the point that they moved him into that competition on the right side. With Sapp traded to Miami on Wednesday, it seems likely that Allen will be the full-time nickel back. If Cook has a strong showing Saturday night, he very well could win that job over Sheppard, who hasn't exactly been impressive in camp.

Defensive coordinator Leslie Frazier said Wednesday that the job is still open.

"Well we want to get through this next ball game and get a chance to evaluate this third preseason ball game," he said. "Chris will get some reps, Asher will get some reps, and so will Lito. And then we will try to put together what we have seen over training camp and preseason games and try to make a decision."

Frazier said Cook and Allen still make youthful mistakes, but that is something the coaches expect to happen.

"No question that still occurs," Frazier said. "And that's going to happen during the season too, unfortunately. That's part of it, because they don't have the experience. The only way you get it is by playing and sometimes making mistakes and learning from them. You can talk to Antoine Winfield, Jared Allen, Kevin Williams, they will all tell you the same thing, first and second year and particularly that first year, things are happening so fast. Then they begin to slow down as you begin to play a little further in your career. There will be some learning. There will be some things that we have to deal with. But they are talented enough that they will learn fast and grow fast as players."

Cook has made several impressive plays on special teams the first two preseason games, including a forced fumble on a punt return in the opener at St. Louis. Special teams coordinator Brian Murphy said he believes Cook can make a significant impact in that phase.

"He's got a knack for it," Murphy said. "You saw it in camp down in Mankato. He just seems to be in the right place, and there's a lot to be said for that. He's a big guy, very fast, he can hold his line in coverage, not afraid of contact. I'm really impressed with what he's done so far, and more importantly he's a willing learner."