Percy Harvin did not take part in today's practice at Winter Park and won't play Saturday in the Vikings' second preseason game at Seattle. The wide receiver has been bothered by sore ribs.

Harvin left practice early on Tuesday and sat out Wednesday and today after originally leaving a practice early on Aug. 8 in Mankato because his ribs were bothering him.

Harvin likely won't travel with the team to Seattle. Tight end Visanthe Shiancoe also will be left behind to continue getting treatment for a hamstring injury he suffered in Mankato. Shiancoe sat out the Vikings' preseason opener as well.

Right guard Anthony Herrera (ACL) was activated from the physically-unable-to-perform list this week but won't play Saturday as the Vikings bring him along slowly. Cornerback Asher Allen (toe) didn't take part in today's practice after doing very limited work Wednesday and coach Leslie Frazier said it's uncertain if Allen will be in uniform against the Seahawks.

Allen's absence would open an opportunity for Chris Cook to grab a strong hold of the left corner spot in the nickel defense. Antoine Winfield would play inside in those situations.

Frazier said Herrera would be evaluated next week to see if he will play in the Vikings' third preseason game on Aug. 27 against Dallas at Mall of America Field.

"He’s had a chance now to kind of get his feet wet a little bit and maybe get his confidence a little bit more," Frazier said, "so we’ll see how he does next week in practice and maybe we’ll give him a shot in that game, depending on how he does in practice.”

Also wide receiver Greg Camarillo will not play because of a groin injury. Harvin and Camarillo's absence would create an opportunity for Jaymar Johnson, Emmanuel Arceneaux and Devin Aromashodu to get long looks as they compete for the fourth and fifth receiver spots.

Others who will be out will be fullback Matt Asiata (hip flexor) and linebackers Heath Farwell (hamstring) and Kenny Onatolu (foot).

Erin Henderson, who is the leading candidate to win the weak-side linebacker's job, sat out today after bumping his knee on Wednesday. Frazier said Henderson should be fine and ready to play Saturday.

Tyrell to get his chance

Frazier said Tyrell Johnson will get the start Saturday at strong safety as the competition for that position continues. Jamarca Sanford started the first preseason game after Johnson missed a couple of days of practice because of a hamstring injury.

"We'll get a chance to evaluate him in a starting role and just continue to evaluate that position," Frazier said.

Ponder to play after McNabb

Starter Donovan McNabb is expected to play a quarter-and-a-half, and he then will be replaced by first-round pick Christian Ponder. Joe Webb was the second quarterback in last Saturday's game and is competing with Ponder for the backup job. Webb will play third Saturday.

Asked what he would like to see from Ponder, Frazier said: "You'd like to see him continue to improve in all areas. His grasp of the offense, some of his throws, his command of the huddle. Those are some of the things you're trying to judge him on and he is making progress. Now, you want to continue to see him in game situations and see how he progresses."

Webb started two of the five games in which he played last season, giving him a bit more knowledge of an NFL offense than Ponder. Of course, the fact new offensive coordinator Bill Musgrave has brought a new system with him means that in some ways Webb and Ponder are about even.

"Joe has some experience at the quarterback position and obviously Christian has none and no experience under his belt whatsoever, so you're at two different spectrums," Frazier said. "But the offense is put together in such a way that Christian has a chance to succeed when he's in there and so does Joe."