Erin Henderson admits he had an instant of intense worry when the back of his left foot was stepped on during Thursday's practice. The middle linebacker's ankle was cut open in the back near his Achilles' tendon and the initial sensation was powerful.

"Really, really painful," Henderson said. "I've been playing ball since I was 7 years old and I've never had anything like that happen to me before. … It was on fire. There was a little bit of fire down there. But once it calmed down a little bit, then I realized it wasn't too bad."

Henderson didn't practice Friday as the Vikings finished up preparation for Sunday's preseason game in San Francisco. But the starting middle linebacker will be active and at full-go at Candlestick Park.

"Nothing to be worried about," Henderson said.

Audie Cole continued to take reps with the first unit Friday in Henderson's place. But the defense should be close to full strength for the first half against the 49ers. Henderson said he's looking forward to the challenge of facing San Francisco's read-option offense after two previous preseason tests against Houston's zone rushing attack and Buffalo's no-huddle, up-tempo packages.

"We've gotten a whole array thrown at us this preseason," Henderson said. "I think it's really good for us as a defense to be able to get some of these different looks and figure out where problem spots might be for us and what we need to work on and what we have to improve upon in order to be ready for the season."

As for Thursday's injury, Henderson also acknowledged he might have dodged two bullets. Just a moment after his ankle was injured, he kicked a cooler out of frustration.

"I think the cooler might have won that battle," he joked. "Actually, I looked down just in time and saw that there was a wet towel. So I assumed it was kind of full so I kind of backed off when I kicked it."

The more you can do

Adrian Peterson showed up at Friday's practice wearing Christian Ponder's red number 7 jersey. It was not, however, a Peterson push to enter the competition at quarterback. At least we don't think.

"I don't know," coach Leslie Frazier said. "That Adrian, now, he's a pretty good athlete. There aren't too many things he can't do. He's always talking to me about blocking a field goal or returning kickoffs. 'Coach, I can be a great punt returner. Let me come off the edge [on defense]. What tackle is going to block me coming off the edge?' There aren't many things he can't do on the football field."

Peterson will see his only preseason game action Sunday. And while he has averaged 12 carries for 59 yards in the Vikings' third preseason game during his career, it remains uncertain how much work he'll see this weekend.

"We'll see how it goes as the game goes," Frazier said.

Cuts upcoming

The Vikings need to reduce their roster to 53 players by 5 p.m. Aug.31 with 15 cuts coming early next week followed by 22 more after the preseason finale against Tennessee. That means internal discussions between the coaching staff, the front office and the team's scouts are intensifying as debate circles on how many players and whom specifically to keep at each position. Sunday's game in San Francisco will further shape the dialogue.

"We're having a lot of discussion about who we need to see, how many snaps we need to see them," Frazier said. "And yet you're trying to balance what you need to get out of your starters as well in this ballgame."

Etc.

• Frazier said receiver Jarius Wright passed the NFL's concussion test and is cleared to return to action. But as a precaution Wright likely will not make this weekend's trip. That will open up additional opportunity for rookie Cordarrelle Patterson to see time with the first-unit offense.

• Five Vikings missed practice Friday: Henderson, Sharrif Floyd (knee), Jerome Felton (appendix), Charlie Johnson (personal reasons), Christian Ballard (personal reasons).