The players aren't the only ones Mike Zimmer is evaluating this preseason. The Vikings coach also has an eye on himself and what he needs to do to improve.

Zimmer has been a football coach since 1979. But since he is a first-year head coach, last Friday's preseason opener was the first game day that he held final say on everything, including clock management, the challenge flag and whether to go for it on fourth down.

Thursday, he said there were two situations in the 10-6 victory over the Raiders that he wishes he had handled differently. The first was not going for a first down on fourth-and-1 early in the third quarter. The other was not throwing his challenge flag late in the game.

On the fourth-and-1, Zimmer said kicking the field goal — a 53-yard miss by Blair Walsh — denied the offense an opportunity to work on a short-yardage situation it had practiced on the first day of training camp.

"If we're going to practice these things, we might as well try them [in a game]," Zimmer said. "And now is the time to try them. It's something we wanted to work on, but I didn't think quickly enough."

As for the challenge flag that Zimmer kept holstered, Zimmer said, "The official on our sideline called the fumble and the official in the back called an incomplete pass. I had three timeouts left and we're winning 10-0 and there's three minutes left. I probably should have challenged."

Zimmer

Cassel locking up job

Zimmer is being careful not to say too much too soon about the quarterback competition. But it's obvious veteran Matt Cassel has moved comfortably ahead of rookie Teddy Bridgewater.

Asked if Cassel will play the entire first half of the second preseason game against Arizona on Saturday, Zimmer smiled.

"Let's see," he said. "The best way to answer that is he has a chance to play the entire first half. Yes."

And, yes, Cassel is expected to start, although Zimmer didn't confirm that.

"I plan on being the Week 1 starter," Cassel said after practice.

No Peterson, Robinson

Zimmer said running back Adrian Peterson and cornerback Josh Robinson won't play Saturday. Peterson, per usual, is being protected from preseason punishment. Robinson, however, continues to battle a hamstring injury that has wiped out most of his training camp.

Zimmer admitted he's concerned about Robinson's role, which initially was to compete for the third cornerback spot and possibly push Captain Munnerlyn in the base defense.

"It's hard to make the club in the tub," Zimmer said. "If you're not going out there and proving it every single day and proving it in the game, it's hard to know."

Step it up, safeties

Zimmer said there are four contenders for the starting strong safety spot that he wants "to take a hard look at" on Saturday. They are Kurt Coleman, who started last week, incumbent Jamarca Sanford, Chris Crocker and Andrew Sendejo.

Zimmer said earlier in the week that strong safety Robert Blanton (hamstring) won't play.

"Right now, I'm looking for the other safety," Zimmer said. "That's why I want to play these guys quite a bit this week. And then figure out the rest of the pecking order."